When a runner is coming from 3rd base to home plate often times the ball gets to the catcher (Guy in the gear) before the runner arrives to the plate safely. The runner can either attempt to slide into the base to avoid being tagged by the ball, run over the catcher in hope that he drops the ball, or turn and run back to 3rd (possibly resulting in a rundown). In the gif it appears that the runner somehow got around the catcher and the catcher is slinging him back off the base in frustration. (Lol idk)