Piscotty-Bourjos collision
 

Last night, (September 28th) in the game between the Cardinals and the Pirates, which is part of a series that will likely determine the pennant race between the two teams, with a 0-0 tie in the seventh inning, two outfielders collided making a catch near the warning track. There were no runners on base, so the out ended playing action.
I'll probably never end up in a play with such implications, but I will likely see outfielders collide violently, and possibly with runners on base. In the referenced play, the player making the catch immediately signaled for help for his unconscious teammate. My question is, if you had seen such a collision, would you immediately stop play and award bases, allow play to continue until its natural conclusion, or something else? What are the approved actions in different rules sets?

Unless you think the player is in danger of getting more injured, then let the play continue.

If someone (trainer, coach, etc.) starts running out on the field to assist, let them, as long as they do not interfere.

Just don't stop play. Everyone else will react as they feel they need to ... but nothing can come of you stopping play for ALMOST any injury at all.

Exception - someone hurt and prone in a location that would possibly have action if play were to continue.

I'm glad I asked. Got two reasonable responses rather quickly.
Normally, I would expect any coaches of youth games to take a sporting response if they realize what's happened.
In light of this incident, my couple years away from the field, and family and friends asking questions, I like to have an intelligent response I can reference.