Shield safety is the term used to describe how advantageous a move is when it hits a shield. It is measured as the difference between when the attacking character can act and when the defending character can act, in frames. Therefore saying that a move is +7 on shield means that the attacker will be able to act 7 frames before the shielder, and if it's -7 then the shielder will be able to act 7 frames before the attacker. if this value is positive, a move is called positive or plus on shield, if it's 0 then the move is called neutral on shield, and if it is negative it is called negative or minus on shield.
Whether a move is considered safe on shield depends on whether the opponent can or cannot punish it, moves that are positive or neutral on shield are safe on shield since the attacker can always act out before or on the same frame as their opponent. Moves that are negative on hit can still remain safe on shield, however more conditions come into play in their case, depending on how fast the other character can act out of shield and the distance that the move is performed at. If the other character can retaliate before the attacker, however the attack will not reach the attacker in time, then the move is safe on shield, hence the importance of distances.
The following spreadsheet contains shield data for most moves in the game under the column Advantage (OOS):
https://docs.google.com/spreadsheet...WFwy_dg04Rrq4a-YF9-VDOhZI/edit#gid=1478544066
Additionally, a specific move's safety on shield under different conditions can be found using Ruben's calculator:
http://rubendal.github.io/Sm4sh-Calculator/
Whether a move is considered safe on shield depends on whether the opponent can or cannot punish it, moves that are positive or neutral on shield are safe on shield since the attacker can always act out before or on the same frame as their opponent. Moves that are negative on hit can still remain safe on shield, however more conditions come into play in their case, depending on how fast the other character can act out of shield and the distance that the move is performed at. If the other character can retaliate before the attacker, however the attack will not reach the attacker in time, then the move is safe on shield, hence the importance of distances.
The following spreadsheet contains shield data for most moves in the game under the column Advantage (OOS):
https://docs.google.com/spreadsheet...WFwy_dg04Rrq4a-YF9-VDOhZI/edit#gid=1478544066
Additionally, a specific move's safety on shield under different conditions can be found using Ruben's calculator:
http://rubendal.github.io/Sm4sh-Calculator/