I would agree with you, I seem to recall there was or maybe still is a station for Watford Football Club, perhaps on the High Street or Croxley Branch, which may be connected to the Met & Jct in the not too distant future.
i also seem to remember going on a train from Manchester Piccadilly to Liverpool Lime Street many year ago and saw a platform for one of the Manchester football clubs, not sure if it's still there and or still used?
Yes, there was a simple wooden affair by the name of "Watford Stadium".
MUFC Halt is still there, but the match day-only train service was suspended recently due to security concerns. Not sure if this is still the case for the new season?