Each team is given a set of systems behind a pfSense or Palo router/fw. The router does NAT from an internal network (192.168.0.0/24) to an external network (10.20.X.0/24).
Competition Networks
Internal team network (LAN) 192.168.0.0/24
Competition Teams (External) 10.20.X.0/24 (where X is team number)