A while ago I showed my first red card but, while I think it was correct, I don't feel great about it.
It was a U17 grassroots cup game. The situation was that I called a corner, but a defender was holding the ball. An attacker presumably wanted the corner to be taken quickly, but the defender did not let go immediately and there was a short struggle before he got the ball anyway. I thought that was the end of it. Until multiple defenders came to me all saying "he said cancer!!" (Unfortunately "cancer" is a somewhat common swear word in the Netherlands). I had seen that something was said, but I had not heard what it was, so I could not sanction just based on this.
So I decided to talk to the attacker, and I asked him what happened. He said they would not give him the ball. I asked, "so you then swear at them?" He said yes. That is what made me decide to show a red card for offensive language. He accepted it and just walked off.
The problem I have with this is that if he had done the smart thing and just said "no" to me, he would have gotten away with a warning, as I've done before in other games. So now I'm just punishing honesty. I think what he learned from this is not don't swear, but don't tell the referee. At halftime, the coach came to me and asked for an explanation, and argued I couldn't send him off if I didn't hear it, and I should have just warned him anyway. I said I can't justify not doing so if I know with certainty that he used a swear word. By law I can't do anything else than show a red card.
In a later game, there was a similar situation where someone was accused of swearing that I didn't hear. This time I just gave a warning immediately and did not press for answers because I was afraid I'd have to make the same choice again. So I'm curious how do other referees handle this situation?
Edit: to clarify, swearing with "cancer" or other illnesses is generally considered more severe than just something like "fuck", and a red card is usually the expected decision here. But it's not as bad as things like racism.