When you play online, look for the connection bars of each player. 1=Bad, 2=OK, 3=Good connection. /=No connection
Never play on 1 bar or /, the bad connection will mean your game will jump and jerk, this is called "lag".
Also lag can occur if you play someone who is cheatng, they cause lag by downloading on their computer while you are playing your match. They can only lag during the half that they host.
If you make a room and participate first(you have a blue dude holding a flag icon), this means you host the first half and are in control of the setup options(weather, match length..etc), you opponent will have a red flag for a 1v1 game, so HE will host 2nd half.
There are lost of complaints about people cheating(lagging), but don't let it bother you. There are FAR more honest players than cheaters.