Weapon and Armor Proficiency
Source: Ultimate Combat, p. 47
A gladiator is not proficient with heavy armor or tower shields. Instead he gains the Performance Weapon Mastery feat (see page 112) at 1st level as a bonus feat. This bonus feat is in addition to the bonus feat a fighter gains at 1st level. Furthermore, a gladiator using piecemeal armor is considered to be wearing a suit of armor as long as he wearing two or three armor pieces, gaining the +1 to armor bonus but still taking the +5% chance of arcane spell failure if the pieces are mixed.