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1.
Football term for the goal. More specifically the net hanging off the goalposts. (soccer if you're american)
'The purchase Agogo dealt on his effort was frightening. He spanked it clean into the back of the onion bag. His goal was a proper hum-dinger and no mistake.'
by thee old boozerooney May 05, 2005
 
2.
The yambag, for Crissakes. What did you think?
My onionbag smells musty--then again, it's 80 degrees. Ballsweat--what a bastard.
by Onionbag January 04, 2007
 
3.
Verb: when a man puts both of his testicles, but not his penis, inside a woman's vagina.
"Dude, I onion bagged Sharon last night. And filmed it."
by Vocabulary Man September 27, 2009
 
4.
1)Extremely large scrotum

2)Football goal netting
1) I've got a proper onion bag

2)I wish that stupid pundit would stop using the phrase "onion bag"
by Football Pundit March 12, 2009