An FA Vase first-round qualifying match was abandoned on Saturday after a spectator reportedly punched a Worthing United player as he was substituted.
The incident occurred 70 minutes into Worthing's home tie against Peacehaven at the Robert Albon Memorial Ground.
Sussex Police say a 24-year-old man was arrested on suspicion of assault, and has been bailed until 3 October pending further enquiries.
At the time the game was called off, Peacehaven were leading 2-0.
"After receiving reports from the game, we are currently investigating the matter but no further comment is available at this time," Sussex Football Association chief executive Ken Benham told the Worthing Herald.
In a statement, Peacehaven said they will be holding a "full investigation into the incident".
Subscribe to the BBC Sport newsletter to get our pick of news, features and video sent to your inbox.