A man was arrested on suspicion of grievous bodily harm after a Reading festival goer had part of his ear bitten or cut off.
The attack happened at Rivermead, behind the festival site, which is hosting late night dance parties after the main acts have finished.
The man was taken to hospital to have his ear sewn back together.
The 35-year-old man arrested at the site was later released on police bail after the victim decided not to press charges.
Overall, Thames Valley Police say crime is well down on last year's festival.
Of 217 incidents reported to police, 90% involve thefts from tents.
There have been a total of 40 arrests so far, mostly for theft, drug offences and for being drunk and disorderly.
Police also say they are concerned at the quantity of counterfeit money and tickets on site.