Four people arrested after jump jockey Aidan Coleman was allegedly punched by racegoers will face no charges.
Coleman, 27, suffered minor injuries, including two chipped teeth, when two people burst into the riders' changing room on 29 September.
A spokesman for Nottinghamshire Police told BBC Sport that no further action would be taken.
It is understood Irish rider Coleman was happy to put the matter behind him, regarding the incident as a one-off.
Two men and one woman were arrested on suspicion of assault and damage, and another woman for obstructing police.
Coleman is second in the jump jockeys' championship, with 84 wins this season, behind Richard Johnson, who has 131 victories.
At the time of the Southwell incident, Coleman's agent Sam Stronge said: "Some lads had seemingly had too much to drink, got a bit rowdy and then broke into the weighing room.
"Aidan was just unlucky - he was the first person they saw and he was just in the wrong place at the wrong time.
"It wasn't anything to do with racing and nothing was said beforehand between any of them."