You can't tell because of the camera angle, but dude's got the dopiest grin ever on his face right now.
A simple picture that just says it all. The vacant but slightly maniacal eyes, the absurd grin, the unquenchable cheer.
And if you think this is just an awkward moment caught on camera, I again direct you to Google Images. This is his facial expression 90% of the time. Swinging the bat (often), throwing the ball, running the bases (rarely).