tl;dr My boyfriend's friend Bill always goes too fast when sparring with me at longsword. How can I tell him that he should slow down or I will refuse to spar him in future?
As a hobby, I do longsword fencing (it's all under the umbrella of HEMA (Historical European Martial Arts)). I've been doing this for about a year and a half at this point, but I'm still not super confident. I have, however, accumulated enough gear that I am able to spar with people with proper protection.
I do this together with my boyfriend, who started doing this because of one of his best friends, let's call him Bill. Now, Bill used to do sport fencing and as such he's pretty confident. He's also been doing HEMA for a bit longer than I have and started sparring long before I got around to it. He and my boyfriend have also participated in some tournaments, at which the level of intensity can get pretty high and minor injuries such as bruises and very occasionally concussions can occur.
I have not started going to tournaments yet, and I'm pretty nervous about doing so. I prefer to spar at a lower level of intensity focusing on technique, as I can't really keep up with faster sparring at the moment due to my reaction times and perhaps partially due to my level of fitness. So, when I spar with people I ask them to go slow.
The problem is that Bill fights very aggressively, and tends to speed up even when you tell him to slow down. When he fights at a higher level of intensity, he can "beat" me easily just by being faster than I am. I find this frustrating, to such a level that one night when I sparred him I got angry, then nearly broke down in tears (although I kept this from him). He fought very aggressively that night, despite my boyfriend telling him to slow down.
A note that should be made is that Bill displays this problem even when sparring with other people. We do something called "slow sparring", which is done without full gear on and at half or a quarter of regular speed. When slow sparring Bill will start slow and then gradually speed up until he is told to slow down again. Rinse and repeat.
I could provide more examples, but hopefully that gets the point across.
In our club, the emphasis is upon being comfortable. So if one person wants to be slower (be it in sparring, drills, etc.) and the other person faster, you go with the slower person's tempo.
Though I wish I could change his behaviour with other people too, for now I would like to focus on how I can help myself to deal with him. In particular, I would like to impress upon him how he needs to put more effort into slowing down when I ask him to, and staying at that level of intensity. If he can't do that, I would like to respectfully decline to spar with him in future, at least until such a point as I can deal with his higher level of intensity. I would like to do this without hurting his feelings, but in a firm manner such that he doesn't try to argue with me about it.