Hi, I would like to know how i would set up a radius damage for a gravity spikes script I'm making, thanks.

The 5th argument of radius damage defines the "attacker"
You could try setting it to the player.

RadiusDamage( Origin, Range, Maximum Damage, Minimum Damage, Attacker );

Indeed it does.

RadiusDamage( Origin, Range, Maximum Damage, Minimum Damage, Attacker );

I've never tested, do you know how that affects coop? If another player is close to them. I'm assuming that if you define attacker and a player can't hurt another player, that maybe it won't hurt other players then, or themselves?

Player can't hurt another player

Ooooookay. Let's rephrase that maybe... I was wondering...

When Attacker is defined in this function, can other players, or the Attacker themselves, be injured from calling this function?

I assume your answer states that it will not hurt other players.

setPlayerIgnoreRadiusDamage(true);

you could use this

setPlayerIgnoreRadiusDamage(true);

As it makes the players ignore radius damage all together but that would mess with raygun/grenades/launchers ect.

When Attacker is defined in this function, can other players, or the Attacker themselves, be injured from calling this function?

I don't need to know, I was curious. Knowing that changes my opinion of the optimal way to damage zombies around. I'm not the op.