Fleeing the scene of what? TM was a guy wearing a hooded sweatshirt in the rain, talking on the phone while carrying iced tea and candy.
Suppose GZ had merely 'detained' him? What would he have thought he was detaining him for? My son wears hoodies frequently. He might walk through a neighborhood at night talking on the phone. Why would he be followed? He's a young man, and young men are occasionally stopped by LE for no reason, just EWY (existing while young).
I fail to see any reason whatsoever why TM should have been pursued, or followed, or detained, or shot. Zimmerman didn't recognize him as someone he knew from the neighborhood. But it looks as though there are 100+ units in the neighborhood- there could be many hundreds of people living there, and it was so dark, how could Zimmerman recognize him, regardless? He followed a teenager who was doing nothing wrong, not even acting suspiciously.