Players lacking hunger on matchday???

Hi everyone.

Does anyone have any tips for players lacking hunger come matchday? This is a sporadic thing with my team, and doesn't show at all in training. It's frustrating because on their day they are a very competitve team, but some games half of them mentally don't 'turn up'.

I feel I'm a very positive coach, who preaches nothing but positivity and uplifting talk. So any advice I'd be very grateful for.

My team are U12s 9 a side.

Thanks!!!