Lightning struck The Ballpark in Arlington during the 4th inning of the game, with one branch of lightning hitting the upper deck canopy followed by a second branch of lightning striking near the center field wall.
You can see the darkening skies off behind Roy Oswalt's shoulder as the video started (look over his left shoulder through the right field stands), indicating a storm was nearby. The game was quickly delayed as players and umpires scurried for cover quickly, with play resuming after nearly 45 minutes. It wasn't the only strike of lightning nearby, by the way.
Nobody (thankfully) was hurt but it was a rather close call...and a reminder to take cover quickly if you hear the sound of thunder while you're outside! If anything, it does call to mind that Major League Baseball's policy about extreme weather is pretty much full of fail...we in Philadelphia have known this since 2008, of course...but the fact that there wasn't a delay for lightning because of the proximity of this storm is kinda worrisome.
Denard would tell you that despite the close call...he thinks (semi-jokingly) that Roy should've been called for a balk for flinching during the lightning strike.