There is some confusion with the construction competitor watch. Specifically, when one needs to talk about monitoring what the competition is up to, is it better to say competitor's watch or competitors watch, competitor watch or competitive watch?
Well, competitor's watch doesn't mean monitoring the competition. It either means a competitor's timepiece or a competitor's effort at monitoring something. The 's denotes possession, in this case, something in the competitor's possession. So this construction is inaccurate.
Competitors watch is just clumsy. If we want an adjective to modify watch, then it's much better to use the root word competitor. Using competitor in this way makes it an adjective modifying the word watch.
The last one, competitive watch, can also be used. Technically, it's a better construction because competitive is an actual adjective so it's the right word doing the right job.
Therefore, if you're talking about keeping an eye on the activities of a competitor, use competitor watch or better yet, use competitive watch.
