The numbers show that Glen Perkins has been an effective pitcher since moving from the starting rotation and into the bullpen. The Minnesota Twins southpaw knows those numbers as well as anyone, and not just his won-lost record, his ERA and his WHIP. He’s also aware of his BABiP, his FIP and his WAR, as well as most anything that can found in his PITCHf/x data.
...On FIP, BABiP and WAR: “I like a lot of stats and go onto FanGraphs pretty much every day. I like FIP and xFIP, which give you an idea of whether you’re doing the right things. Not that it’s something you can control, but you know that if it’s down — and you keep doing what you’re doing — the balls are going to find fielders. If your FIP is one thing and your ERA is higher, they’re probably going to meet in the middle. My ERA this year started out high and came down to closer to what my fielding-independent is.
“I didn’t get frustrated with my bad ERA. I had given up a couple of home runs and felt that maybe some balls were finding holes. You can’t start thinking, ‘Now I have to strike every guy out.’ Understanding that things should even out gives me confidence in what I’ve done. [FIP] shows that I should be here, and not here.
“I do get a little frustrated with my BABiP. I’ve always had a high one, and it’s high again this year. I also don’t have my ground-ball rate down, but I’ve focused more on fastballs up in the zone and sliders down in the zone. Last year, my two-seam and four-seam were a more even distribution. It’s more four-seamers this year, so I’m getting more fly outs.
“I like WAR, but I don’t like it for relievers. I think it’s a good stat for starting pitchers and everyday players, because it’s a bulk stat. I don’t think you can quantify relievers the same way you can quantify a starter. You need to break off them into a separate group to see where they stand. My numbers as a reliever are going to be different than they were as a starter.”