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1.
(n) A vibrator or other sex toy a woman may resort to if her partner (the "starter") can't finish the job.
She was so frustrated -- she had her relief pitcher go for 18 innings.
by Bill Peters November 17, 2006
 
2.
For males engaging in a sexual act with a woman: An alternate source of stimulation used when the currently enacted source of stimulation becomes tiresome to the male giver. The act of switching from vaginal sex to digital stimulation would be considered "bringing in the relief pitcher." Often used to conceal physical weakness and to the female recipient is seen merely as "switching it up." Can help maintain pleasure levels. Keeps manhood in check.
"dude i was bangin' my girl so hard but i got fuckin' tired so i brought out that relief pitcher son."
by Random Ock March 24, 2009