I found the easiest time to get this achievement was during Case 1-4, right after the cutscene at Everyone Luvs Books.
1) Grab a parasol, one of the large blue umbrellas, that are near the escalator.
2) Walk back outside to the Al Fresca Plaza, and begin running with it through the crowd of zombies.
3) As this needs to be done in a single run, keep up your momentum by avoiding obstacles like walls or the fountain, and hold down the run button. Continue to knock zombies aside until you see the achievement pop at 30 hits.