I'm not convinced starters need 5 days rest anymore. I think they could go to a 4 man rotation if starters aren't getting past the 5th inning.

One of the commenters at FG article mentioned that 25% of active pitchers in MLB have had at least 1 TJ surgery.

Anyone know where I can find this data ? That's higher than I thought for some reason.

If starting pitchers are becoming obsolete, I say let's get rid of the whole pitcher specialization thing. You field 9 players, and each has to pitch one inning.

That's the crux. The best (only) rationale for going to a 6-man (or better, 6-day) rotation is to take innings away from relievers. By definition an expanded rotation reduces the number of starts your top guys get but if it allows them to go deeper into games then it doesn't need to decrease their total innings.

Top starters have lost about 20-30 innings over the last decade or so already. In 2000, the #10 in innings was 227; in 2010 it was 224. In 2019, the league leaders was 223 (#10 at 204) and that was a bit higher than 2017-18. Replacing innings pitched by #4-8 starters with innings from #5-12 relievers probably does make sense; replacing innings pitched by #1-3 starters with innings from #5-12 relievers surely does not. Using a 6th starter to take another 20-30 innings off your top 3 guys does not seem wise.

Realistically in today's usage, they're probably not going to be allowed to eat up more than about 125 innings in their starts anyway. Assuming they'll stick with the 13-pitcher limit, a 6th starter necessarily needs to replace a reliever slot which is a min of 75-80 innings. You then want each additional inning to also come off a reliever or your #4/5 starters, not a top 3 starter, so the top 3 need to go a bit deeper into each start. That might improve your staff overall. But it might not -- most of those relief innings replaced are low-leverage ones; maybe you've got a #6 that's OK but somebody will still get hurt and you're gonna need #'s 7 and 8 still and you don't want to be giving them more starts.

To the extent we'll see this, I would guess it will be one of two models. First might be a 6-day rotation where the top 5 SPs always get 5 days rest but, if there's no game on one of those 5 days, then one of the back of the rotation guys gets skipped. A strict 6-man rotation would limit the top guys to just 27 starts and you'd have to push them out to 7 innings to get a "full" season out of them, I don't think that's happening. With a 6-day rotation, you can probably get that up to about 30 planned starts (down from 32-33). In this model, the 6th start could be a bullpen day.

The second model we might see is to go to a 6-man in stretches with few days off or the height of summer -- sort of a variation on the 6-day. Maybe 13 instead of 16 starts from June through August will avoid some dead arms and/or keep guys more effective in Sept. Or not. If you're pretty comfortable that you are (or are not) making the playoffs, then you can keep it going in Sept. There's also the "Dodgers model" though you need a big payroll (or excellent pitching development) to pull it off. For the last few years, they've tended to have 6 (even 7) good but fragile SPs under contract, presumably with the notion that usually at least 5 of them are healthy at any given time. On those rare occasions you find yourself with all 6 healthy, you go to a 6-man rotation. (I think the Dodgers have mostly avoided a 6-man in those circumstances.)

I see two possible trajectories:

A) 4 man rotation with the starters on strict 80-90 pitch counts, plus two "bridge guys" to pitch innings 5-6 if necessary and connect the starters to the short relievers.

B) True six man, similar to the Japanese setup, where the starters are expected to face 30+ batters and complete games are a thing again, but they get a full week of rest.

I think trajectory A makes a lot more sense. The batters get progressively better when they see a pitcher multiple times on the same day. You can probably train pitchers to improve endurance to pitch a whole game but that doesn't help them fool the batter. If the pitchers never see more than 18 batters then they shouldn't need a week to recover. A day should be sufficient. Pitch/recover/conditioning day/recover. Ditch the 5th starter and go with a 9 man bullpen. Get more innings out of your best pitchers by pitching them more often.

A day should be sufficient.

Was that a typo? The history of the days when a reliever might have 50 appearances and, say, 120 innings is that they broke ... a LOT. Pretty much nobody withstood that sort of workload for more than a few seasons. If you meant 3-4 days should be sufficient then OK.

People forget/don't know but Gossage only had 3 relief seasons with substantially more than 100 innings; only a couple more around 100. Fingers managed 1150 IP over 9 seasons, appearing 65 times a year.

A few guys of course managed 37-40 starts a year and 270+ innings on a regular basis so we clearly can't rule out that the stud aces could handle 40/200 or 50/200 these days but you're not pushing them past that. And remember, even for somebody like Scherzer, twice through the order is 4.5 innings. Even with openers polluting the data, the average 2019 start lasted 5.2 innings, 22.1 BF. Nobody is looking to add a further 162 innings to the bullpen load.

3-man rotation with 18 batter maximum. Bring in the starter after 2 innings since they can’t go more than 6 anyway. Have a fourth and fifth “B-tier long men” who pitch instead if the results of the first two innings suggest and uncompetitive game to give an extra day to the rotation on occasion.

Pretty much nobody withstood that sort of workload for more than a few seasons.

not disagreeing, but.....

Mike Marshall famously won a Cy Young Award (and finished 3rd for MVP) for the Dodgers in 1974.

stats: 106 G (all in relief), 208 IP, W-L 15-12, 2.42 ERA, league-leading 21 SV

this is the meat in a sandwich, all in relief, of:

1972 - 65 G, 116 IP, W-L 14-8, 1.78 ERA, 18 SV
1973 - 92 G, 179 IP, W-L 14-11, 2.66 ERA, league-leading 31 SV

1975 - 58 G, 109 IP, W-L 9-14, 3.29, 14 SV

he then faded - but bounced back with stellar seasons in 1978-79 at age 35-36 in 242 total IP and 2.45 and 2.65 ERA with 53 more SV

4 year peak of 612 relief IP, 52-45, 84 SV, strong ERA

Marshall turns 78 on Friday, and I remember him well - and I'm not even 60.

8 seasons of solid 99+ IP of relief

I think many baseball fans under 40 may not have heard of this outlier fellow - who also got a turn as a 1969 Seattle Pilot in Jim Bouton's iconic "Ball Four" book.

The phrase "pretty much nobody" would seem to allow for "one here or there."

But Mike Marshall only made it to 1400 career IP of 118 ERA+. Scherzer is already to 2350 IP of 132 ERA+. Why would you risk turning Scherzer into Marshall? Wilhelm is the main counter-example with 2250 IP and a 147 ERA+ but that was probably due to being a knuckleballer ... although the IP total could have been much higher if he'd made the majors before 29. Fingers made it to 1700 innings.

#8: Why? What advantage is gained? How does shifting 4/5 starter innings to the pen help? Do folks not realize that reliever and starter ERA have been in rough equilibirum since 2018?

You are at least shifting some innings to those top 3 starters which might work. Probably more innings than you think though (more than I thought). Your model would put them at about 900 batters faced in a season. Maybe you'd have enough of those bullpen days that you'd get it down as far as 720 (40 appearances each on average). In 2019, only one pitcher topped 900 BF -- Bauer. Only 21 faced 800+ batters, only 60 faced 700+. It's far from clear that increasing their workload while giving them fewer days off won't break them more often. In theory, if you keep their workloads the same then you haven't lost anything -- you're still spreading those other batters across 10 pitching rostter spots.

A day should be sufficient. Pitch/recover/conditioning day/recover.

A day between the start and their throw day. 3 days off between starts, 85-90 pitch starts.

How does shifting 4/5 starter innings to the pen help?

It's about getting more out of your top 4 starters. Do you want 33 starts of ~6 innings from your top starter where they're pitching the 3rd time through the order 33 times or do you want 40 starts of ~5 innings where they never face the order a 3rd time? Then you have 9 (or more depending on the AAA shuttle) relievers available to finish the game.

I just hope whoever signs Bauer lets him go every 4 days. Lets shift back to that. In 1982 for example, the Jays did a 4 man rotation (top 3 had 38/40/38 starts, 23 for the #4 guy, 23 for the rest). The big 3 all had double digit complete games and 249 2/3+ IP each. The big 3 were Jim Clancy (26 years old) and he had another 1541 innings, 95 ERA+ left in him (4 years over 100 ERA+). Dave Stieb (age 24) and he made the next 3 All-Star teams, very solid starter to age 32 before his arm went kabloom. Luis Leal is more what we all expected (age 25) as he only had 3 more seasons, last only half a year. Strangely his next 2 were ERA+'s of 100+ and that final year the Jays gave up after just 14 starts, 74 ERA+ and he never came up again (2 more years in the minors). #4 was Jim Gott who was a 22 year old rookie (23 starts, 136 IP, so not too hard a push) but was 'meh' around 100 ERA+ until moved into the pen. He had a 14 year career.

Now that is a very very limited check, but probably as recent a team to do a 4 man all year (some experimented for a month or two but not a full season). After 38 years I think someone should give it a shot again.

obligatory Ted Lyons homage:

never pitched in the minors, White Sox 1923-42 and 1946.

a life well lived

1073 K in 4161 IP, lowest rate of any HOFer since 1920 - and he ain't giving this one up anytime soon.

averaged 274 IP from 1925-30, going 112-90, an average of 19-15 for generally bad teams.

arm blows out, knuckeball/slops his way to 16 K in 101 IP in 1931 with a 106 ERA+.

then averaged 221 IP for three decent years, but never pitched 200 IP again as manager Charlie Dykes lightened his workload. started only 20 to 24 games from 1935-42, mostly on Sundays - hence the "Sunday Teddy" nickname.

In 1942, a 42-year-old Lyons went 14-6 - completing all 20 of his starts - and led the AL with a 2.10 ERA and with a 171 ERA+.

then - single and without dependents - he joined the Marine Corps and remained out of MLB for 3 years, serving mostly as a fitness instructor but also playing in some overseas All-Star games with the likes of DiMaggio and Ted Williams.

Lyons returned in 1946, completing all 5 of his starts at a 2.32 ERA at age 46 (but a 1-4 record). then, upon being named manager, he retired as a player - completing his final 28 starts.

who is a current candidate to be "Sunday Teddy?"

Hamels? Kluber? Strasburg? (kidding on the last one. probably.)