Here come the excuses:
At the long end of the lens.
Sun in front of me.
Fill flash doesn't go that far.
My dog was tugging me in the other direction.
Grumble, grumble.......I'll get it right one of these days!
When you forget your shooting the D5100 and the dial isn't set up the same as the D7100 I went from (on the D7100 SS of 1/1600 to on the D5100 SS of 1/250)