Dave Hagewood helped incorporate the Onslaught mode into Unreal Tournament 2004. Before Rocket League, Hagewood and the Psyonix team experimented with rocket-powered vehicles in Unreal Tournament, work that led to an official vehicle-focused game mode.
Onslaught was an objective-based multiplayer mode built around vehicles, large maps, power nodes, and team combat. Players fought to connect and destroy opposing nodes, making it substantially different from standard arena deathmatch. Unreal Tournament 2004 officially introduced the mode along with a range of drivable vehicles and specialized weapons.
This history is part of Rocket League’s origin story. Hagewood’s earlier vehicle experiments helped establish the technical and design foundation that later evolved through Supersonic Acrobatic Rocket-Powered Battle-Cars and, ultimately, Rocket League. Invasion, Domination, and Assault were separate Unreal Tournament modes.