There are six types of concussions: vestibular, ocular, fatigue, anxiety/mood, migraine headaches and cervical. Each of those concussions’ symptoms has different triggers. For example, symptoms of an ocular concussion, which affects visual tasks and the ability to track moving objects, can be prompted by being in the bright light of a cellphone or being in a long passageway, Collins said. The Yankees have not said what type of concussion Frazier has.
Each type of concussion has distinctive therapies.
“If you can have 30 different types of knee injuries, why do we think there’s one type of concussion?” said Collins, who added that each type of concussion has about 20 subsets. “There’s different treatment to those different problems. Science is progressing rapidly now that we know it’s not a homogeneous thing.”
As diverse as the treatments might be for a concussion, they are almost all active, involving some sort of exercise or exposure to conditions that might exacerbate symptoms, Collins said. What is important is not pushing too far or easing off too much.
“It’s a brain injury; it takes awhile to recover,” Collins said. “But it’s a treatable problem. The best way to prevent concussions is to manage it effectively when you have one.”
Though concussions are typically associated with high-impact sports like football or hockey, or in a sport that requires heading a ball, like soccer, they do occur with some frequency in baseball. The Yankees, for example, have had a player get a concussion in six of the last seven seasons.
An ocular concussion can be significant for a baseball player, given how it impacts vision. “Try to hit a 95-mile-per-hour fastball with really good eyes,” said Collins, who treated the former Yankees infielder Stephen Drew when his 2015 season ended with a concussion he received after being hit in the face with a ground ball.
Research is indicating that even when players return from a concussion, their performance lags in the weeks upon their return. Erin Wasserman led a study of the performance of players who spent time on the disabled list with a concussion between 2007 and 2013, and used as a control group players who went on paternity or bereavement leave.
Wasserman found that batting average dropped 31 points, slugging percentage declined 62 points and on-base-plus-slugging percentage fell by 99 points in the first two weeks upon players’ returns from concussions. Performance was still lower four to six weeks after returning, but not significantly so, Wasserman said.
Credit Kathy Willens/Associated Press
“The symptoms and neurocognitive computerized testing is all we have to measure whether an athlete is recovered, but the neurocognitive areas that are required for hitting may not be fully recovered,” said Wasserman, a sports injury epidemiologist at the Datalys Center for sports injury research in Indianapolis. “We didn’t find any evidence that it was dangerous for these players to return, but there may still be some sort of deficit.”
That may help explain why Yankees center fielder Jacoby Ellsbury, who missed a month with a concussion last season, experienced a sharp decline in his performance when he returned, leading to his eventual benching.
Ellsbury was having a solid season, batting .281 with a .771 O.P.S., when he crashed into the center-field wall at Yankee Stadium making a catch. In a little over three weeks between his return and his benching, Ellsbury batted .177 with a .497 O.P.S.
Ellsbury declined to be interviewed for this article, but General Manager Brian Cashman said that Ellsbury’s decline after the concussion was not a surprise and that it was explained by a neurologist last season.
“It’s almost like a period of time they’ve got to work through on their own, regardless,” Cashman said. “You have to grind it out and be patient.”
Eventually, Ellsbury found his peak form, hitting .337 with a .912 O.P.S. in September.
A tipping point in how baseball began to view concussions came 10 years ago with Ryan Church, a Mets outfielder whose career was derailed after he was allowed to continue to play for about a week despite experiencing symptoms from his second concussion in a two-month period. After a steep decline in performance, Church retired after the 2010 season at age 31.
His case spurred Major League Baseball to develop a concussion protocol, which was updated in the most recent collective bargaining agreement in 2016. It requires baseline testing of players when they enter professional baseball and dictates what tests must be administered before a player can return. It also allows for a seven-day concussion disabled list, removing an incentive for teams to keep players off what was then a 15-day disabled list. (It has since been shortened to 10 days.)
It also calls for a game to be stopped and a player to be evaluated on the field by a trainer if there is an incident that carries a high risk of concussion. If the trainer detects signs of a concussion, the player must be removed and examined further. But because a concussion’s cause can be so nebulous, it is hard to know just what constitutes a high-risk collision.
For example, Ellsbury was allowed to remain in a game last May after running into the wall at Yankee Stadium to make a catch. But when he was re-examined at the end of the inning, he was removed from the game. He missed a little more than a month.
It is not clear how Frazier became injured. He fell backward making a catch on Feb. 24 in Bradenton, Fla., and his head hit the wall. A trainer did not examine him until he came off the field at the end of the inning. Later in the game, Frazier caught a ball on the warning track and his shoulder hit the wall, jarring him. He did not begin experiencing symptoms — a headache and nausea — until after the team returned from Bradenton.
Frazier has undergone a CT scan and an M.R.I. and has visited regularly with a league neurologist, as well as one in the Tampa area.
After Frazier spoke with reporters last Saturday, expressing his frustration that the symptoms had improved but had not cleared up, he was barred by Cashman from speaking to the news media.
Cashman pointed to the N.F.L. and the N.B.A., which make their players off limits to the news media while they are recovering from concussions.
Asked when Frazier, who had come to spring training motivated to make the opening day roster, might get back on the field, Cashman shrugged.
“No one can predict that,” he said.