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1.
A contest between male rivals to see who can swing their nuts back and forth the fastest without using their hands. The fastest moving sack wins the race
Edgar clearly showed his dominance over Jonny by swinging his sack at an astonishing speed and winning the sack race.
by DLF June 08, 2005
 
2.
1) The fierce, unspoken competition between men to each prove themselves to be the alpha male of the group.

2) A competition between friends to see how quickly they can get someone in bed.
Greg and John are neck and neck in their sack race, as Greg has bagged himself identical twin girlfriends, equalling John's threesome with 2 glamour models.
by MagickDio August 28, 2010
 
3.
When someone runs a race with their nuts or testicles out of their pants.
Yo man i sack raced Tom and i won,with my nuts out on the street.
by Panouch March 10, 2008