When he could not endure the cruel ragging any longer, the new recruit bravely stood up to all his bullying seniors.

challenged : used to indicate that someone or something is lacking or deficient in a specified respect.
fought : take part in a violent struggle involving the exchange of physical blows or the use of weapons.
resisted : withstand the action or effect of.
defeated : having been beaten in a battle or other contest.
stood up to : to defend yourself against a powerful person or organization when they treat you unfairly.

Synonym of stood up to is resisted