I tried googling this question and I have not found the answer. I am watching A Knight's Tale, and while I know it is entirely fictional, I was wondering if the stirrup was used when jousting was first introduced as a sport, anywhere across Europe. I do not know enough about this era to know when stirrups were introduced, but I do know they were invented in China and spread westward, if I am correct. So I do not know if they coincide.
The Bayeux Tapestry depicts stirrups, an example of which can be seen clearly here. The stirrup was adopted by the Byzantine Empire even sooner than that, and there's an argument to be made that medieval mounted warfare as we know it was only possible because of the invention of the stirrup. Source
On another note, it would have been very difficult to joust without stirrups. Stirrups improve balance and give a rider something to brace on, so that they can better absorb the shock of a blow. When you use stirrups, your feet kind of "dig" into the stirrup so that you're not just sitting on the horse's back like a sock monkey-- you're settling your weight into the stirrups. Without that assistance, it would be extremely difficult to use a lance and nearly impossible to brace for the blow of being struck by a lance.
