Interrupt Attacks are melee attacks that stun or stagger an enemy preventing them from doing anything for a short time.
There are two levels of severity that a player can be stunned by: light and heavy. A light stun causes a Marine to appear as though he is flinching. A heavy stun lasts longer, and the Marine visibly staggers.
Generally, Interrupt Attacks executed later in a combo (e.g. Attack-Attack-Stun) have a longer range and/or area of effect and induce the staggering heavy stun, compared to Interrupt attacks earlier in a combo which will have a shorter range and only cause a light stun.
The damage of Tactical Marine stuns: backhand 35, kick 40, shoulder bash 25, stomp 75.