You can only activate this card if both you and your opponent each have 5 or less cards on the field. The maximum number of cards that each player can have on the field is 5.
Rulings
Individual Card FAQs
If "Spatial Collapse" is activated, and an effect is chained so that a player has more than 5 cards on the field after "Spatial Collapse" resolves, the controller selects cards to send to the Graveyard to make the number 5.
You can activate "Spatial Collapse" when you have 5 or less cards on the field and your opponent has 5 or less cards on the field.
"Spatial Collapse" includes Tokens, too.
While "Spatial Collapse" is active and you have 1 or more cards already on your side of the field, you cannot activate "Scapegoat" because you would have your 1 previous card + the "Scapegoat" card + 4 monster tokens = 6.
When you have 4 cards on your side of the field while "Spatial Collapse" is active, you cannot activate "Change of Heart".
When "Cyber Jar" is activated while "Spatial Collapse" is active, if the number of cards exceeds 5, each player selects cards to send to the Graveyard to make the number 5.
When you have 4 cards on the field and you activate "Remove Brainwashing", you select cards to destroy to make the number of cards you control 5.
Netrep Rulings
While “Spatial Collapse” is active, cards that Special Summon a monster may not be activated if that player's filled zones are 4.
The zones prohibited by “Ground Collapse” do not count toward the affected player's limit for “Spatial Collapse,” unless a monster already occupies that zone.
Trap|
Continuous