infield fly
 

runners first and second one out, on contact runners take off fly ball infield
umpire calls infield fly. Ball is not caught , do runners have to retag or keep running.

No tag up required. it's a drooped fly just like if it had been to an outfielder. Only exception is that the batter-runner is still out on the called IFF.

The ONLY difference between an infield-fly-by-rule and any other fly ball is that the batter is out automatically, caught or not.

Runners do have to tag if and only if the ball is caught in flight.