McCoshen played in 38 games for the Florida Panthers in 2017-18, his first full NHL season, finishing with four points (three goals, one assist), 43 blocked shots and 71 hits.
The defenseman, a native of Anaheim, California, was taken by the Panthers in the second round (No. 31) of the 2013 NHL Draft after three seasons with Waterloo of the United States Hockey League and was named to the 2012-13 USHL First All-Star Team. McCoshen played the next three seasons at Boston College, recording 50 points (17 goals, 33 assists) in 110 games. He also played for the United States at the 2014 and 2015 IIHF World Junior Championships.