If a monster wont to charge a target in the back ranks but a fighter stops him with combat superiority before he can reach his target (which is not the fighter), can the Monster attack the fighter instead since it is the only enemy in reach?
Another reason to say no: that's the fighter's schtick. Don't gimp it.
Isn't there a Fighter interrupt that deliberately lets you do this? i.e. take the hit of a charge

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.