1) One who is depended upon to complete an integral function of a larger task, but fails in a manner which nullifies the efforts of the others involved

2) One known notoriously for "dropping the ball" (see above) often.
"Ok, joe can get the keg and rich can make up the posters"

"wait, Joe can't get the keg, hes a ball dropper, have bill get it instead"

by Meredith July 16, 2003
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A seller who sells something he doesn't have. Usually someone who plans to by locally with the buyers money and make a profit. Either the final bid is lower than the local cost, or the merchandise isn't available . Asking for a shipping date usually results in insults or threats but no shipping date.
Getting what I paid for from that ebay ball dropper was like pulling teeth.
by mikie the yorkie March 15, 2008
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