Share stock
Sharing stock, also known as life stealing, is the action of transferring a remaining life to a fallen teammate who has no more lives. This puts the character back into action, with one life, and removes one stock from a team member. This is initiated, by the defeated player, by pressing Start/Pause in Super Smash Bros. and Super Smash Bros. Melee and A+B in Super Smash Bros. Brawl, Super Smash Bros. 4 and Super Smash Bros. Ultimate when out of lives. Naturally, this can only be done in a team stock match, where a teammate has more than one stock remaining. In Melee, the announcer will say "Stock Player Removed" when this is performed after pressing start/pause button. In both Brawl and SSB4, the announcer will say "Share Stock!" ("Share Player Stock!" in the Japanese version) by pressing the A and B buttons together. In Ultimate, he will instead say "Restocked!"
If a team has multiple living players, the stock will be taken from the lowest-numbered player. And if multiple players tried to steal a stock simultaneously when there aren’t enough stocks for everyone, port priority determines that the lowest numbered player gets the stock.
In Super Smash Bros. 4, CPUs will always take a teammate's stock at every opportunity until no more are available. When the game was released, CPUs would take the stock immediately after dying; a later update introduced a realistic delay. In other games, CPUs never use the share stock function, although players can manually have CPUs share stock in Melee by pressing start on a controller connected to the same port as the defeated CPU.
Strategy
While it may seem like a simple decision, many factors should be taken into account when choosing to share stock. Firstly, it is wise for team members to discuss or ask permission before stealing a life, not only as it may be considered rude not to do so, but for strategic purposes. For example: If one were to steal a life from a teammate with two stock, but a high damage percentage, this would essentially be similar to swapping lives, as they're likely to be KO'd soon afterward. Of course, communication is not always possible during online matches, so sharing stock in these instances may be more of a personal decision.
One should also take the stage into account when determining whether or not to share stock. Large stages like Temple allow partners to survive to much higher damage percentages, while smaller stages like Final Destination don't.
In tournament doubles, one of the two players on a team is often designated as the "stock tank", typically whichever is controlling the character with higher survivability or better camping. General strategy then revolves around the stock tank playing a defensive role, while the other player plays offensively, borrowing stocks as necessary (as they will be KO'd more often), as being caught in a two-on-one with two stocks is worse than having a two-on-two with one stock each.
Transport glitch
The transport glitch is a glitch in Super Smash Bros. Melee. If one team member has lost all of their lives, the other teammate jumps a little higher to where the character would re-appear after falling. Then, the screen is paused, and the defeated teammate simultaneously life steals. If performed correctly, the character that was defeated should instantly appear on screen when the game is unpaused.
