“Everybody says it’s bursitis,” Johnson said. “I thought if he took some anti-inflammatory it would calm it down, but it’s kind of been lingering. When he runs it swells up. He was jogging in the pool it swelled up from that. We’re concerned so we’ll get another opinion on it.”

One possibility Johnson acknowledged was Harper getting the bursa sac removed. His bursitis is due to swelling in the bursa sac in his left knee.

A person’s head collides with an object. Unprepared for the impact, the head jerks in a violent whiplash motion. The person collapses, rolling on the ground and holding his head, before rising slowly and unsteadily. Eyewitnesses testify that the person was confused or disoriented.

“By definition, that’s a concussion,” says Dr. Daniel P. Perl, a professor of pathology at the Uniformed Services University of the Health Sciences in Bethesda, Md., the American military’s medical school. “A concussion is a transient loss of neurologic function following a blow to the head. Typically it can be confusion, memory loss or loss of consciousness.”

That’s what happened to soccer star Abby Wambach last month when she was hit in the face by a speeding ball, and it’s what happened Monday when Washington Nationals outfielder Bryce Harper ran face-first at full speed into the outfield wall at Dodger Stadium. “Initially, it was like he was confused,” teammate Denard Span said. “I don’t think he realized he was on the ground.”

A spate of suicides and diagnosed cases of dementia involving retired N.F.L. players has prompted research to determine whether there is a correlation between constant blows to the head, which are endemic to football, and a degenerative brain disease known as chronic traumatic encephalopathy.

Testing of brain samples drawn from deceased former players by the Boston University Center for the Study of Traumatic Encephalopathy has found that 33 from the N.F.L., along with 17 who competed at other levels, suffered from C.T.E.

With [Ryan] Freel, the center enters the realm of baseball, a sport not usually associated with head trauma. His parents approved the donation of tissue to search for evidence of C.T.E., which might partly explain his decline as a consequence of the injuries….

Based on the recollections of the player’s mother and Ryan Freel’s own statements, his stepfather, Clark Vargas, estimated that Freel may have sustained 15 concussions, 10 as a professional ballplayer…

Freel’s former wife said she found no fault with his teams or their medical staffs, concluding that they diagnosed his condition properly and insisted that he abide by the stipulated recovery period…

Freel had consulted with doctors and had had examinations, mostly psychological, according to his former wife, and even became aware of the C.T.E. studies. “He sought answers to his problems,” she said.

Yet he did so reluctantly, according to his mother. She indicated he would not always heed her advice to seek help from doctors or counselors and was especially reluctant to carry through with follow-up appointments…

Freel’s mother dropped by his home on the Friday before Christmas and, noticing that he was not feeling well, urged him to visit a counselor. He agreed to do so the next Monday, she said. His body was discovered the next day…

Christie Moore Freel acknowledged that the head injuries might not fully explain why her former husband took his life. “Ryan had a lot of battles, fought a lot of demons,” she said.

He was arrested at least once for drunken driving and on another occasion for disorderly intoxication.