Arm Wrestling is an arcade video game by Nintendo released exclusively in America in 1985. It is a spiritual successor to the Punch-Out!! series, and is considered a spin-off, even featuring one of the characters of the series, Bald Bull, as one of the opponents (under the title "Mask X").
In Punch-Out!! for the Wii, Doc Louis will give Little Mac tips in between fights. One of the tips he gives Little Mac during his fight with Bad Bull (the sole Punch-Out!! character to appear in Arm Wrestling) is to try and arm wrestle with him. This is an obvious reference to the character's appearance in Arm Wrestling.