On turret target acquired is a TRIGGER. This means, when 'it' happens, the event runs. How to explain.
Say you have 5 events and event nr 3 is a trigger. You could think they run sequentially. First event 1, then 2, then 3, then 4, then 5 .... and again 1. But the trigger happens when 'that thing happens' where it is designed for. No matter wich event is running, event 3 will run, when triggered.
As a result, at that one moment a target is acquired it runs, and if you force it to acquire a new target in the same event, it runs again, and again, and again. Because that is what you want it do. It is, in fact, CALLING itself. So, after a while, this CALLING itself, exceeds the CALL STACK.
Say, you code something like .... on the moment i open a door ... do this. And this 'do this' is: open a door. At that moment the 'on the moment i open a door' kicks in. Because that is what you just did, open a door. This is calling itself.
Sorry, it is so evident to me, and so difficult to explain.