Challenge
Is there a proper way to challenge someone to a sparring match?
Answer: Thank you for your post and sorry for the delay of my reply.
If a person whom you want to do jigeiko (sparring) with is sitting, go up to him/her, sit in seiza, bow to him/her and tell them you would like to have a jigeiko with him/her.
If a person whom you want to do jigeiko with is already a motodachi (receiver), just place yourself 9 steps away from him/her and bow when he/she is ready to fight you.
If a person whom you want to do jigeiko with is standing, go up to him/her and bow in your standing position saying that you would like to have a jigeiko with him/her.
We do not challenge like we used to do in the old days. We ask others to train with us.
Hope this helps.