Is it legal to shoot a Welshman with a crossbow in the city walls before 9 am on Sunday morning?

No, it is not legal to shoot a Welshman with a crossbow, or anyone else for that matter, regardless of the time or location. Such an act would typically be considered a criminal offense, including assault or attempted murder, and would be subject to severe legal penalties. Laws regarding weapons and violence apply universally and do not provide exceptions based on specific conditions like time or location.