Matthew Stafford getting hit where it hurts was actually a gift to his wife ... 'cause she joked the blow below the belt he suffered in Sunday's game against the Eagles was a free vasectomy!!
Kelly -- who married Stafford in 2015 -- had the funny take about the Rams quarterback on her latest episode of her "The Morning After" podcast ... and she explained what he told her about the third-quarter incident after the loss.
"He goes back in [to the game], thank goodness, and after the game, I'm like, 'Hey, what was going on.