Listening to the original dispatch tape, Zimmerman is on the phone to dispatch, he gets out of his truck to make contact with what he believes is a kid acting suspiciously (at this point nobody knows the name of the kid). The kid walks towards Zimmerman. Zimmerman is relaying all this to dispatch.
At some point, the kid takes off running. Zimmerman then takes off running after the kid. Zimmerman's breathing becomes rapid, you can hear it on the tape. The dispatcher asked if Zimmerman was following the kid, Zimmerman answered "yes." The dispatcher tells Zimmerman, "we don't need for you to do that." Zimmerman answers, "ok." From this point on, Zimmerman's breathing slows down (you can also hear it on the tape), he's not running after the kid any longer.
Following the kid is ok, keeping an eye on the kid is ok, running after the kid was not advisable and Zimmerman stopped.