Multiattack. The gladiator makes three Spear attacks. It can replace one attack with a use of Shield Bash.
Spear. Melee or Ranged Attack Roll: +7, reach 5 ft. or range 20/60 ft. Hit: 11 (2d6 + 4) Piercing damage.
Shield Bash. Strength Saving Throw: DC 15, one creature within 5 feet that the gladiator can see. Failure: 9 (2d4 + 4) Bludgeoning damage. If the target is a Medium or smaller creature, it has the Prone condition.
Parry. Trigger: The gladiator is hit by a melee attack roll while holding a weapon. Response: The gladiator adds 3 to its AC against that attack, possibly causing it to miss.