What is the pun in this joke "The first time I met my wife I knew she was a keeper. She was wearing massive gloves" by Alun Cochrane
In football / soccer1 (goal)keepers wear oversized gloves:
If a person you are in a relationship with is decribed as a keeper it's someone considered to be held onto, someone "you should keep".
The joke plays with the double meaning, in a classic example of a double entendre.
1 and other sports involving a ball and a goal: (ice) hockey, cricket, lacrosse... Not all sports, though, e.g. water-/handball are played "gloveless".
It is a play on words based on
a) "Keeper" Urban Dictionary Definition
a term used to describe a guy/girl that you love very much and plan to "keep"
b) "Keeper" Oxford English Dictionary Definition See #2
Shorthand for a Goalkeeper (Football [UK]) or Wicketkeeper (Cricket)
who would traditionally wear large gloves:
The first part of the joke leads you to believe that the teller is talking about definition a), but then qualifies it by talking about the gloves to give definition b)