When you attack a (lower level?) player (maybe several times) the game bans you and your allies from attacking that player again for 12(?) hours. The problem with this is (as I believe it it implemented) is that that player may attack your tribes different players as many times as he wishes. So, your tribe attacks him 'several times' and he attacks your tribe maybe 20 times in that 12 hours period.
I would suggest that the limit be changed to a 'you (your tribe members) may attack a player once (maybe several times) PLUS the number of attacks made by that player on your tribe in a 12 hour period". I would think a rolling 12 hour window would be better but it could be implemented differently to lessen server load.