to have partied to hard to the point where you are to sick to continue the party. To sit your ass on the grass refers to having bit off more than you can handle while partying, and being unable to party anymore.
Ex. 1 - Man I had to sit ya ass on the grass the other night you went to hard on the alcohol.
Ex. 2 - I sat your homeboy on the grass the other night, he thought he was tough enough to hang with the big dogs.
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