I have 6 Harlequins in my 20g. They spar like that quite frequently. I always assumed that it's a kind of dominance ritual, that they are sorting out their "pecking order." I've never had any jump outs.
I don't have a lid. I used to have floating water sprite, but I got rid of it a couple months ago. I've had the 6 Harlequins in my tank for a bout a year and a half. They are very active, but they have never jumped.Do you have a lid? Failing that, do you have a lot of floating plants? Both can reduce incidents of jumping dramatically, and you may want to try them if you want to get more rasboras.