10:47 a.m.
Police tell Philly.com that it was an unexploded firework.
10:42 a.m.
According to FOX Philly producer Kyle Carmean, the worker indeed hit a rock and it caused a spark. All clear.
10:32 a.m.
According to 6 ABC, the bomb squad has been called to Citizens Bank Park.
At around 9:45 a.m., a worker cutting grass outside the stadium struck something that the worker claims “exploded,” according to the report. He wasn’t hurt.
Police are there now. One has to wonder if the worker hit… a rock.