Coach and captain of the local blitzball team,
the Besaid Aurochs. Wakka plans to retire from the sport
after this year's tournament, so that he can devote
himself fully to serving as Yuna's guardian. His deadly blitzball
is especially useful for knocking down aerial enemies.

To simply put, Wakka is pretty weak.
His only usefullness comes from attacking aerial fiends.
He has skills that cause status ailments on all creatures which
can help out at the beginning of the battle before switching to the
more balance and powerful fighters like Tidus and Auron.