Collin Finnerty, 19, of Garden City, N.Y., was sentenced to six months' probation after a two-day trial.
The judge also ordered Finnerty to submit to drug and alcohol treatment if probation officers deem it necessary. During his probation, Finnerty also must stay out of any establishment where alcohol is served unless accompanied by his parents, and must stay out of the Georgetown neighborhood, where the assault occurred.
Finnerty could have gotten six months in jail; prosecutors did not ask the judge to impose jail time.
Prosecutors said Finnerty instigated an attack on two Georgetown bar patrons in the early morning of Nov. 5. One victim, Jeffrey Bloxsom, testified that Finnerty pushed him, threw fake punches that landed within inches of his face and hurled homophobic epithets.
Superior Court Judge John Bayly said he believed Finnerty was guilty of "menacing" Bloxsom as part of an assault, though it was a friend of Finnerty who admitted punching Bloxsom. Finnerty's two friends admitted criminal responsibility but avoided prosecution under a special program for first-time offenders.
Finnerty's attorney, Steven McCool, said he will appeal the conviction.
"Judge Bayly found Collin Finnerty guilty of simple assault because he threw fake punches ... and because he scared one of the complaining witnesses in the case. That's it," McCool said.
Finnerty declined to speak after the trial or to address the judge before receiving his sentence.
Among those who testified for Finnerty was former Duke lacrosse captain William Gerrish. Gerrish testified that he saw Finnerty get punched in the head, though he had previously told police that he never saw Finnerty get hit.
Finnerty, Reade Seligmann and David Evans are charged in Durham, N.C., with raping a woman at a March 13 team party where she was hired to perform as an exotic dancer. All three have said they are innocent.