Thanks.....on further thought, it seemed strange to us because he clearly blew his whistle, indicated a scrum (and the reason for it) before any throw in was taken.
No option was offered and his call for the scrum could only have put off the Castres players who were as surprised as we were...............
I can now understand the law and the proper interpretation but still feel, in this particular circumstance, and they way the ref handled it, it was wrong to allow it to proceed.
The least he should have done, in view of his error iin signifying a scrum, was call them back and THEN offered them the option on basis of fairness to both sides.
As it happens the move broke down and there was no advantage in the end but there could easlily have been had BO held on to the ball...........