The Mets announced that catcher Travis d'Arnaud has a sprained left elbow. Earlier today, they placed him on the disabled list and called up Bronx native Johnny Monell to take his place on the roster. At that time, the team indicated that d'Arnaud had been sent back to New York for further examination by team doctors.
We're not doctors here, but here's what the U.S. National Library of Medicine has to say about elbow sprains:
A sprain is an injury to the ligaments around a joint. When you sprain your elbow, you have pulled or torn one or more of the ligaments in your elbow joint.
Here's the play on which he was injured:
When healthy, d'Arnaud has been one of the Mets' best hitters—and one of the best-hitting catchers in baseball—this year. In 77 plate appearances, he has hit .296/.338/.535 with a 143 wRC+. Unfortunately, he had missed over a month after suffering a broken finger when he was hit by a pitch earlier in the season, so he has been off the field more than on it thus far.