I'm planning to spike the visiting team's room food service with laxatives.
Will doing that to their food make them sick?
Only if they are constipated.
Feeding people laxatives without their consent is wrong since it will make them very physically uncomfortable and could possibly lead to incontinence. You should never adulterate anyone's food. If you are upset at the visiting team, you should compete against them fairly and with sportsmanlike behavior and not through underhanded tactics like giving them laxatives.
This is a prank. How am I not supposed to prank my rivals?
This prank could be taking things too far. You should never mess with people's food, even if you are just trying to prank someone.