I'm really upset so please be gentle if I am being unreasonable.
I had a call from Ds1 school today to say he'd had a break down (her words) in PE today. He was in such a state that the pastoral leader was called to calm him and she took him off to her office for a couple of hours.
The crux of it is, he's being bullied and today a comment about him probably not being strong enough to throw shot put as he was stepping up to take his go just made him snap and weeks of incidences and problems that he'd been bottling up just came flooding out.
He's been chosen by his house sports captain to run a race that he will almost definitely come last and he's so emotionally that I know it will make him cry on the sports field. Adding fuel to the fire if you will.
School are being very good. The pastoral leader has already spoken to the children involved (ironically these are his friends!) and referred Ds1 to a one to one therapy course in school aimed to boost his self esteem and support his emotional wellbeing. We are also working on this at home.
So would you (and should I....) keep him off school for sports day? I know it isn't right to avoid things we find hard but I just can't put him through it. 
Forgot to say he is 12, yr 7 but we are in a three tier system here so not at secondary (for some reason this always comes up when I talk about my children's schooling and I get moaned at for not mentioning it).