Description (c) cpma docs:

Hoonymode is a novel form of 1v1 play, loosely based on tennis rules.
All in-game behaviour (weapons, physics, items, etc) remains the same
as standard DM: the change is in how the game progresses from one frag
to the next.

During warmup, two spawnpoints are chosen by the players. One will
typically be a "stronger" spawn and the other "weaker". When the game
begins, these are where the players will spawn, with the strong spawn
considered the equivalent of having the "serve".

Each player death (regardless of source, i.e. a suicide is considered
a kill for the opponent) is treated as a distinct point. After a point
is scored, play does not continue as in DM: instead, the players and
the arena are reset, and a new point is contested for. Players switch
spawnpoints at this time, so the player who had the weak spawn for the
previous point now has the strong one, effecting a change of serve.
Players are given a few seconds between points to reconsider strategies
etc.

Games are played to a point limit, with the clock not being a factor.
A player must reach that limit and be at least two points clear of
his opponent to win, i.e. in a 5-point game, 5-4 is a lead not a win:
the player still needs another point to clinch it.

Implementation Specifics:

Players claim a spawnpoint by moving near it and using the spawn
command (via console/bind/etc).

Referees can choose spawnpoints for players by using "spawn <pid>"
(Players can also use this when playing bots).

Players are not FORCED to choose a spawnpoint: spawns will be random (not
recommended).