No one would have guessed that Peregrin Took would help save Middle Earth, much less prove himself a competent warrior. When we first meet the youngest member of the Fellowship, he's a clumsy, absent-minded prankster, but by the end of The Return of the King, he is a Knight of Gondor. During the Battle of the Black Gate, Pippin steps up in a big way, helping lead the charge and drawing Sauron's attention away from Frodo in Mt. Doom.
That said, Pippin never makes any big kills or has any standout moments on the battlefield. Though a good fighter, he never shifts the tide of battle, which is why he ultimately ranks towards the bottom.
For a character who primarily functions as comic relief, Pippin shows some serious battlefield prowess. However, he can't compete with some of the Fellowship's heavy hitters.