Can a coach sign an agreement instead of the client?

Yes, by logging in as the client (in Contacts > Contact Name > link "Login as {Client Name}" > go to the client's Agreements page on the private portal). As a good practice, the client should be informed in advance about the agreement and is informed by being sent the agreement email. The coach can sign the agreement instead of the client only after it is emailed to the client. Agreement drafts cannot be signed.