Sometimes your only options might be to kill yourself on a turret, monster or minion. How long from the last time an enemy attacked you until you die does it have to be for it not to count towards your enemy score? I belive it is called an execution when you do this.
If a champion dies and hasn't been damaged or debuffed by another champion in the last 13 seconds, it is an execution. Otherwise, the kill is awarded to the enemy champion who last dealt damage.
Executions are generally caused by a turret, minion, or monster. An execution offers no gold but still gives experience to nearby champions on the opposite team.
Also from the Wiki like 2 inches further down.
So basically, if you exhaust an enemy champion at 12 seconds after the damage you dealt it gets reset. The only way for them to dive a tower or minion wave and commit suicide is if it has been 13 seconds since any enemy has inflicted any kind of debuf or damage.
Short Answer 10 seconds;
- Assist is when you helped the Killer kill a champion with heal or buff or de-buffs or damage.
- The Killer is the person who last hit the the opponent champion.
- But when the Killer is a neutral unit like a minion, monster or a turret, the Killer becomes the last person that assist the kill the champion.
So for example when you use Mocking Shout (Tryndamere) in an enemy champion and he died for a turret (let's say he lost ALL health 100% to the turret).
- If you have shouted with the last 10 seconds before the last hit occurs. you get the kill for yourself;
- If you have shouted AFTER 10 seconds, the kill goes to the turret (execute)
I Could not find a link to Mocking Shout, so here is the skill description:
"Mocking Shout = (Active): Decreases surrounding enemy champions' attack damage, and enemies with their backs turned also have their movement speed reduced for 4 seconds. No cost Cooldown: 14 seconds Radius: 400"
Source "A kill is the act of decreasing another champion's health to zero while it has no abilities to prevent death. The last player to strike the target champion is awarded with the kill, and all contributors within the last 10 seconds are awarded with an assist."