How to deal with an over bearing parent

So I reluctantly stepped forward to coach/manage my son's U8 team. It has taken me completely out of my comfort zone but we're three matches in and I have to say I'm loving it. I don't have an assistant yet so am doing the coaching and managing myself. This is all new to me and it's the first year the boys have played in a league so new to them as well. We've yet to win a game but we keep smiling and I ensure I encourage the boys to just have fun whatever the outcome. My issue is one of the dad's. Every match so far he stands on the sidelines shouting at the boys telling them what to do and where to stand. He is contradicting what I'm telling the boys and what I'm trying to encourage them to do during the match. Being a man his voice carries further than mine. This weekend he surpassed himself. After one of the quarters my team were standing on the pitch waiting for the other team so they could start the next quarter. This dad ducks under the respect line, runs onto the pitch and moves the boys to where he thinks they should be. It completely undermined me in front of the kids, parents, opposition and referee. My question is have you dealt with something similar and if so, how without causing a fall out? Any suggestions greatly received. Thanks. Gemma