Okay, so a player went down. On easy or normal, just crouch, shoot around the player and you can easily pick them up without worrying. However, advanced and expert is NOT that simple. Crouch (obviously) and attempt to pick the horde off of the player. If they have high incap hp, back up a bit and shoot from a distance. However when they have low incap hp (100 hp or less) get in there and shove the commons off if you can!

If you have grenades, use them WISELY!

Pipebomb: Use these pipes when the player is boomed while down, or if a huge, HUGE horde is after them. It won't bring them ALL to the pipe, however it will attract some of them and numbers matter, remember that. Throw it somewhere that makes sense. Not too close and not too far will help out.

Bile: Please....just please do not use this when an incap player is boomed (or whenever a standing player is boomed). It doesn't do anything, it just doesnt. However, you can use this when an event is going on. For example, Dead Air at the airport run. Throw it at a far place then quickly pick up your friend. (I just remembered that if you throw the bile at a zombie while someone is boomed, it works! So do that when people are boomed who are trying to help your friend.)

Molly: Only use this when a player is for sure going to be dead. Use this when a huge horde is on the incap player and he/she has 50 incap hp. That's all i gotta say basically haha.

Simple: run to a safer spot. Once that horde gets off that player, they'll come after you. If you know for sure they'll die anyways, just save yourself and go to a far away spot.