Spting Glitching..?

i really have no idea how to explain this.. so basically i go on this server: play.mcsn.us and go to kitpvp.. so i have to run around and spring and jump and all that.. so when i get people hitting me and im sprinting the game puts me on one block and untill i stop moving it keeps pulling me back.. so i have to stop mid battle or running.. just so i can move.. and its really annoying..