As seen in THQ's WWF Wrestlemania 2000, and WWF No Mercy for the N64. Normally, when one lands the low-blow, a "PING!" sound is heard. The struck character then does a funny walk grabbing their junk, leaving them open for a follow-up hit.
See also: Double Nut-ping Cancellation
:: one player low-blows another on No Mercy:
"AWW! Dude, you nut-pinged me!"