Yes, that is
a tornado (apparently not a tornado but just a really scary stormcloud) beyond the left-field wall at yesterday's opening night for the double-A Frisco RoughRiders. It was part of a series of storms that swept the Dallas area, and resulted in the RoughRiders' game being postponed in the third inning because of "rain."
The above photo was taken by Fox 4 News; here's another one from the guys at Rangers podcast Baseball Do:
And a couple more ridiculous weather photos from the DFW area: