A motivation spank occurs when you spank your partner/spouse/friend/colleague to show him/her support and to encourage him/her to take some difficult effort.
"Go Tigers! The trainer shouted loudly in the locker room and spanked the quarterback loudly in his bottom."
Wife: "Honey, I'm not sure I'm gonna perform well on this interview."
Husband: "You'll do great, I'll give you a motivation spank!" <<Slap!>>