That was X and he tweaked a knee, or groin, or hammy, or something about 5-10 minutes earlier going for a ball on Kent's baseline. He fought through it the rest of the game and I think he was just letting his guard down, being a little melodramatic & nursing that (minor🤞) injury.
EDIT: As I rewatch the above video, it looks like he may have simply had a charlie horse in the calf.