One special weapon appears particularly on the Scottish side of the Borders and that is outlined here;
https://doi.org/10.1163/9789047407577_023
Thus 2 alternatives ...the one being the Jeddart (Jedburgh) Staff and the other the Lochaber Axe.
The article suggests that it was not used to unhorse an opponent but more to hang the weapon on the wall...It seems there were two versions ...The Jedburgh Staff and Lochaber Axe and you can decide if it was useful? ...I think it was ... and as the Border Reiver had a lot of straps on weapons and riding gear... hooking him off his horse would seem to me as very possible. assuming you could get inside lance or sword etc...
Peter Hudson.