If something puts you off your stroke, it stops you from concentrating on what you are doing, so that you do not do it as well as usual. A sudden sound from behind me put me off my stroke and I missed the ball completely. Compare with put someone off their stride. Note: The reference here is to rowing, in which all the members of a team have to pull on their oars at exactly the same moment. Each pull of the oars is called a stroke.