Abstract. A synchronous game semantics—one in which several moves may occur simultaneously—is derived from a conventional (sequential) game semantics using a round abstraction algorithm. We choose the programming language Syntactic Control of Interference and McCusker’s fully abstract relational model as a convenient starting point and derive a synchronous game model first by refining the relational semantics into a trace semantics, then applying a round abstraction to it. We show that the resulting model is sound but not fully abstract. This work is practically motivated by applications to hardware synthesis via game semantics.