Darren Weir, 22, admitted to the offences in Cardiff
Darren James Weir, 22, of Pimlico, central London, admitted breaking the girl's jaw on 27 December last Christmas after a concert by the group in Cardiff.
The judge said he was not handing down a jail sentence in order to preserve Weir's career prospects.
But his victim's mother said: "It's a disgrace - he should have gone to jail."
So Solid Crew comprises more than 20 DJs, producers and vocalists, including the duo Oxide and Neutrino, who have had their own chart hits.
Sexual advances
The incident took place at a Cardiff hotel close to the Vision 2K nightclub where the group had been performing as struggling garage artists.
Prosecuting, Meirion Davies said the band members agreed to give the girl and her friends a lift home at the end of the night, but said they needed to stop at the Ibis hotel on the way.
But, in the early hours of the morning in the hotel's foyer, the girl slapped Weir in the face after he had made sexual advances.
Mr Davies added: "He punched her in the face - she was floored by the force of the blow.
"Weir ran out of the hotel leaving the girl bleeding from a mouth wound. All the girls were screaming."
The punch broke the girl's jaw, which later required the insertion of three metal plates.
'Responsibility accepted'
At the time of the attack, the victim had not known the identity of her attacker.
She recognised Weir on a television music channel, then bought one of the band's CDs, with his name on, and told police.
"You have expressed shame, regret and remorse, but make no mistake, if you're back in court again, your career will be at an end.
"You are a young man on the brink of a career which may be extremely successful - we do not know.
"I am satisfied on the evidence that a prison sentence would undoubtedly have a significant adverse effect."
But the girl's mother added: "If it had been any old Joe Bloggs it would have been a different matter - he would have been jailed."
So Solid Crew's manager Albert Samuel told the court Weir was essential to the success of the group, which is due to release an album next month.
He said he was currently negotiating deals worth thousands of pounds to the artist.
Award winners
Relatively unknown until recently, So Solid Crew have won three Mobo awards this year and had a number one hit with the single 21 Seconds.
The collective won awards in the categories of best UK garage act, best newcomer, and best video - for Oxide and Neutrino's Middle Finger.
But crew members have been associated with trouble before. Ashley Walters, 19, has been charged with making threats to kill.
The group came together when 21-year-old MC Megaman, who had been promoting UK garage parties and performing in nightclubs, got together with MC Romeo, 20 at the Killer Watt carnival sound system.
The success of the group comes from their fresh mixture of R&B, hip-hop and ragga sounds.