Simple dumb watch. A tenner down Argos, should last you ages.
Fitbit or Garmin for the fitness watches with stopwatch capabilities. I only suggest them as they have a battery life of up to 4-5 days. Apple is apparently awful for battery life. Trouble is, the watch versions will set you back £200+, so bear in mind you're getting it for the heart rate, steps counting etc. Doesn't matter if it's 100% precise, it's just data to give you some estimates.
Alternatively, you could just go with two dumb-watches and one fitness tracker.
If you're new, I wouldn't be making such an investment into the fitness tracking/watches just yet. If you're not new, or you know you're staying in the refereeing circuit for a long while, then they're handy tools for your own benefit if you are happy to track the data.
And if you have absolutely no interest in fitness tracking, then two basic watches from Argos will do you good until retirement probably.