A runner on 1st should be holding up halfway to 2nd on a fly ball to the outfield so unless he prevents a triple, which he should score on anyway, I don't see how a runner could clog up the bases. Maybe a guy at 2nd when there is a really fast guy at 1st prevents an extra base. I guess I don't see it having much of an effect unless he gets thrown out taking an extra base, but that would also go under poor baserunning. I guess if you are poor at base running you could clog up bases, but to me that would have more to do with being a good base runner, which I personally think could be taught, than speed. EDIT: Think of Carlos Lee as an example of a good base runner who had very little speed. 2nd EDIT: I thought of a better example. Miller gets a single. Weeks hits what would normally be a triple, but Miller is only fast enough to get to 3B. Miller on 3B, Weeks on 2B, with no outs. Or would you rather have, Miller pops out. Weeks hits a triple. Weeks on 3B, one out.