Opponent wants to abandon.

[BodAndrage]

I've got a game of checkers on the go and my opponent had requested to abandon after just a few moves but not said why (I've asked).

If they said why I'd be more inclined to accept.

What's your opinion on these things? Is rejecting the abandon as they did not give a reason, so they would have to quit instead the right course of action on not sporting?

[Jest Phulin]

In my opinion, refusal to follow through on the commitment to play a game is the most unsportsmanlike action listed so far. It is not unsportsmanlike to refuse a request to abandon with no explanation, especially in a 2-player game. If the opponent does not wish to continue the game, they can concede. OK, yes, in order to concede 50% of the game must have been completed first. And, there can be language barriers. "Yo, mate, what'cha want to abandon for?" is harder to mechanically translate than "please explain why this game should be abandoned." But the belief that someone can start a game, and if they don't like an aspect of it propose to abandon, and that proposal must be accepted is the belief that their time is inherently more important than their opponent's. While a human's time is more important than an AI's, and most computer games can be abandoned with this belief, this is not the situation on this site. Human players are not interacting with artificial intelligence, but with other humans. It is not unsportsmanlike to remind them of this, and refuse to abandon without explanation.

[Ankeszu]

I agree with Jest Phulin.
And yet while I agree that request of abandon with no explanation / because of mistake in the game is not sportsmanlike, I can consider agreeing to abandon - and privately to never play with the requester again. Why even consider agreeing? Abandoners usually make the game highly not enjoyable when you refuse to abandon... So it depends on if I am in the mood to be ok despite even more rude behaviour.
(In real time there is also another useful option - switch to turnbased.)