Bat Boy Kaiser Carlile -- Dies After Taking Bat Swing to the Head

A 9-year-old bat boy died in a freak accident at a baseball game -- Kaiser Carlile was struck in the head by a batter in the on deck circle.

Kaiser suffered the fatal blow on Saturday during a semi-pro summer league game in Kansas. According to reports ... he had just picked up the bat from the previous hitter ... when the player taking practice swings accidentally hit Kaiser.

Carlile was wearing a helmet. He reportedly initially fell down, stood up, but quickly collapsed again. He was rushed to a Wichita hospital, but died on Sunday from his injuries.

Kaiser was bat boy for the Liberal Bee Jays of the National Baseball Congress (not affiliated with MLB) ... and the NBC said, "Kaiser was simply doing something he loved. He was simply doing a job most kids across America dream of having for one night or multiple summers."