A teenager's father and brother were attacked when gatecrashers turned up at his 16th birthday party.
Chris Worthy's parents had granted permission for about 30 guests to come round to the house in Chippenham, Wiltshire.
His 18-year-old brother Stephen Worthy was present but events spiralled out of control, leading to six arrests, police confirmed.
Stephen was taken by air ambulance to hospital, but later released.
The brothers' father, David, 53, was also attacked.
A Wiltshire Police spokesman said: "A number of uninvited guests turned up and the party was stopped.
"Two people were arrested on public order offences, and four on suspicion of grievous bodily harm."
"Investigations are continuing."