A cross-up is the act of timing an attack (typically a dash attack or aerial attack) such that the user moves past the opponent and ends up behind them once the hitboxes are gone. Dash attacks are the more common kind of cross-up as the user is moving quickly already and many give the user additional propulsion. Short hop back aerials are a common cross-up as well, with the user starting in front, then short hopping over the opponent, followed by a back aerial as they go over the opponent. Cross-ups could be considered a kind of approach, but they can also be used to perform mindgames. The idea of the technique is that the attacker cannot be shield grabbed when behind the opponent, which makes such attacks safer to use by removing a common option from the defender. However, some characters have moves that strike faster against targets behind them, such as Mario's up smash, making the technique risky in such cases. Examples of attacks that can be used to cross-up include Fox Illusion in Melee, Brawl and SSB4, and Snake's dash attack in both Brawl and Ultimate; with proper spacing, such attacks can put the user behind the opponent and end with the user in a less vulnerable position for punishment. This technique can be done repeatedly to rack up damage if the opponent does not react properly, although it can still leave the user in an extremely vulnerable position if abused.
In Super Smash Bros. Ultimate, several grounded attacks that could perform cross-ups can no longer do so (or are less likely to do so) due to the altered jostle mechanics. Additionally, some other moves, such as Fox Illusion and Heel Slide, have been adjusted so that they cannot cross up against shields, making this strategy useless with such particular moves. However, many attacks can still perform cross-ups despite this; these include several dash attacks, such as those of Ganondorf, Snake and Wolf, in addition to certain down tilts, such as those of Cloud, Min Min and Sephiroth, and even some special moves, such as Falcon Kick, Wonderwing and Quick Attack. With the use of a roll cancel boost grab, some characters can perform a pivot grab that causes them to end up behind an opponent; however, this is dependent on the character used.