catch- used when confronted by a scary object, mob, gang, or something you don't want to do is about to happen, it CAN mean goodbye, but like this, you don't actually go anywhere, you just remain standing or sitting, sometimes said or pronounced, 'cyatch'.
It can also be said just before it would seem you will get hit by a car.
(Zac is standing in the middle of the road)
(a car comes flying around the corner)
(car turns away from Zac)
Toby: Yo Zac, see that gang of Crips over there?
Zac: yeah man, catch! (Zac remains walking with Toby and never stopped walking)