The wallrunning bug can occur when the player runs along a north-south wall (either normally or by straferunning) while touching it. Occasionally, in this situation, the player suddenly finds himself accelerated to a rather greater speed than he can normally attain; this lasts until he stops running, encounters a corner, or changes direction (e.g. by being hit by a monster).
An agile player can exploit this bug as a speedrunning or deathmatch tactic, taking advantage of north-south walls to dodge projectile attacks or move quickly between distant areas of a map. Its use in deathmatch play is somewhat limited, however, because it requires that:
- the level contain a straight north-south wall in the appropriate place(s);
- the player figure out which way is north, possibly during a fast-moving firefight;
- the player rapidly orient himself at the desired angle to the wall (either precisely along it, 38.7 degrees away, or 45 degrees away); and
- the player then wait a moment for the acceleration to begin.