After reading it, seems like his b moves hit with his bat, and score bases. Every time you get 3 bases, they combine to give a home run. Every 11 runs gives you a victory cry power up which buffs moves and stats.
I gotta look into clean hits, balls, and strikes though.
Clean hits happen after the 11 run buff. You have to hit the person with the bat at a "decent spacing" apparently.
http://www.dustloop.com/wiki/index.php?title=Junpei_Iori_(P4AU)
Anyway, yeah the Tarot Cards and Bop Bag were included with the game for all pick-ups. Good move, Atlus. *thumbs up* the Tarot cards were bigger than I expected. I expected them to like... Magic: the Gathering/playing card sized. But whoo~
Now to hope the Standard version of Persona Q includes them so I have both sets. >_>