Leadership is an attribute which only has an impact in many vs many battles (team battles). It does not do anything in a 1v1 battle. This is usually a less important attribute for gladiator but can nonetheless be very valuable in team battles, clan battles etc. You can see which gladiator was the “leader” of a team in a battle report.
Leadership increases initiative, dodge, taunt and weapon skills for all of your teams members. The player with the highest leadership value in a team will increase attributes and weapon skills for all other players in the team and in turn receive a boost from the player with the second highest leadership value.