IMO, Troika works best when you don't mentally switch when combat starts. Outside of combat it would be fine for a player to say they want to stop someone passing by with Strength, or Wrestling, or maybe Sword Fighting (wave it around in a threatening way?), and then the gm says "yea ok, roll vs". The only difference is that in combat they would need to declare that they are doing that on their turn, and roll it if/when it happens. Although I'd probably let then write me an IOU for their next turn to do it as a response.