The coach of the Challenge Cup won't sign it. You can try to communicate with the teacher or find another teacher to sign. According to relevant public information, if the instructor of the Challenge Cup refuses to sign, first of all, we should respect the teacher's opinion and don't force the teacher to sign. He can try to communicate with the teacher, explain the importance of participating in the challenge cup and ask the teacher for help. If the teacher is still unwilling to sign, you can ask the relevant departments of the school for help, or find other teachers to sign for you.