From The TimeSplitters Wiki

Max Damage is a glowing red sphere that contains a spiked ball that looks similar to a WW2 anti-ship mine. It temporarily yet dramatically boosts the damage dealt out by the player's weapons. With this power-up, pistols kill in just a few shots, and automatic weapons are capable of cutting through entire groups on enemies in moments. Like all power-ups, it is only available in TS2 and TSFP's arcade and mapmaker.