Drinks were thrown over a family while they were at a horse race.
A man and two women from Hampshire were in the Lennox enclosure of Goodwood racecourse when the dousing happened at 5.35pm on Friday, August 1.
They were on the grass area in front of the stand near a bar tent.
Police say they were not injured.
Sergeant Neal Harvey said: "If you can help provide names or descriptions of the people responsible please contact us via firstname.lastname@example.org call 101 quoting serial 1487 of 1/8."