Jeremy Renner -- Back at Work After Ax Brawl

Jeremy Renner was flanked by security on the set of "The Bourne Legacy" ... just a few weeks after that crazy ax brawl in Thailand.

Renner looked unscathed and unfazed by the bizarre incident -- where Jeremy and some buddies threw down with six bar employees ... one of whom busted out a homemade ax and slashed one of Jeremy's friends.