The fight goes on while the menu is open.
The harbour is one big floating dock. Pick your fighter, take your knife, and be the last one billing. Toss a lobster trap, wait 5 seconds, then eat the lobster for +1 HP (max 3) or throw it at a rival to get them fired. Wool suits do not float.
Choose your fighter
Bots
Play with friends
Make a room, then send the link to your friends. It stays open while anyone's in it.
Walk and turn with the arrow pad, and press STAB to fight. MENU explains the other buttons.
Playing solo against bots.
Pick a key to change it, then press the new one. Esc cancels, and Backspace clears it.