Tree Swallow Stare

I often come across birds I don't recognize, this small one was flying around a baseball field, I had not even considered trying to take his picture he was very fast. But on my way out of the park, I noticed he'd landed on a fence and stayed there, while I crept up on him, I got fairly close before he finally decided that was enough and bolted. If anyone can identify this one, please let me know.