All depends,
How old is the perc?
How big is your tank?
How long has the perc been in the tank?
Overall, if the perc is young(under a year) and you just put the perc in within the last few months. the perc and maroon will just be territorial. BUT... When they both are mature adults THE FIGHT IS ON!!!!!!!!!!!!!!!!!! Unless you have a 200+ tank with lots of hiding spots