Yes, if his move hasn't completed yet. This is exactly the same as
attacking someone who's moving. The check will be made on day 7.
> If I cast the barrier on day 1, and he moves on day 9, will he still be
> considered to be in the province, and trapped, when my barrier goes up on
> day 10?
No, this check is only made when movement starts, so he will not be
affected. The Lords of the Crown experienced this in Orianna, I think.
-- greg