Substitution Rule

[Deftone20]

I have misplaced my ASA Rule Book and of course, you can't get one online so I need some guidance. Can someone explain to me the substitution/pinch runner rule? We are currently in our end of season city tournament and I watched the team that we play next last night. During their game, they substituted their power hitters each inning with a fast runner, and then re-entered the hitters the next time they came up. Is this legal? I saw it at least 5 times. The rule in our league is one pinch runner per game unless otherwise agreed upon by the opposing team. What is the rule for substituting in this capacity and a players re-entry into a game. I need to be ready for this should it come up tomorrow night.

Thanks - Joey