Leicester centre Manu Tuilagi was told on Wednesday night he could have been facing prison and not just a five-week ban from rugby had his attack on Chris Ashton occurred on the street.
Tuilagi punched England wing Ashton three times in the head during Leicester's Aviva Premiership semi-final victory over Northampton last Saturday. The 20-year-old World Cup prospect will be suspended for Leicester's Premiership final against Saracens on May 28 and the England Saxons' entire Churchill Cup campaign.
Rugby Football Union disciplinary chief Judge Jeff Blackett described Tuilagi's actions as "very damaging to the image of the game", and warned Tuilagi he would have been prosecuted had the incident occurred off the field.
The RFU's three-man disciplinary panel made their decision after taking a number of mitigating factors into account, including Tuilagi's age and guilty plea.
Ashton, who required stitches to a cut above the eye, was also deemed to have provoked Tuilagi into throwing the punches.
Blackett said: "This was a top-end entry offence because there were three punches, the third of which was extremely forceful and caused significant injury.
"However, we also determined that there was some provocation from Chris Ashton who pushed and struck him in the back with his knee.
"The top-end range is eight to 52 weeks and we determined that the appropriate entry point within that range is 10 weeks. This was reduced by 50% to reflect Manu's youth and inexperience, his admission of guilt and his genuine remorse.
"This sort of incident is very damaging to the image of the game and there is no place for this type of offending on the rugby pitch. Had it occurred in the high street an offender would have been prosecuted in the criminal courts.
"Nevertheless we are confident that Manu Tuilagi will learn a valuable lesson from this."