Full-strength fighter question

[Dross]

You could try swarms or critters with DR.

Negate his movement: grease, hold person, web, difficult terrain, height and reach weapons.

(along the lines of other non-bash solutions) sinking boat, broken wheel on cart.

When the PCs talk to people for whatever reason, have them ignore the fighter so they can talk to a brother cleric, a fellow mage etc

 

[Alexander123]

It shouldn't actually be that hard.

Also, if your other players don't know how to play casters that might contribute to fighters overshadowing the other players.

What most DMs worry about is casters overshadowing non-casters.