Being able to play requires the skill to effectively Stand your Bakugan on the right Gate Card and battle. If a Bakugan is shot and does not Stand, it is considered a Miss and is put in it's owners used pile.
When two Bakugan Stand on a Gate Card, the Gate Card is activated. Whichever player's Bakugan is more powerful after applying the Gate's power to both Bakugan is the winner of that battle. However, if one player Stands two of their own Bakugan on a single Gate Card, that Bakugan is moved to the other Gate Card. If there is not one, the card is automatically captured with no battle.
What happens when you miss?
The rules are not very clear on this, and there are at least four official answers:
1. Core rules
You miss, the Bakugan goes to your used pile, and it is the next player's turn. Comment (SG): This does allow you to deliberately miss so you go after your opponent and gain a tactical advantage by chosing a Bakugan to react with based on what your opponent rolled. Compared to the other options below, however, this is probably the least susceptible to manipulation.
2. Arena rules
The Battle Arena quick play sheet contains a specific rule: if you miss, then you remove the Bakugan you rolled from the field and place another gate card down if you have one; then it is the other player's turn..)
Comment (SG): These rules could lead to stalemate -- if you both miss a few times then you could end up with all six gate cards down, one Bakugan on each, and nothing to do. Also, even just one miss would negate the possibility of capturing a card by standing two Bakugan on it, as a player only has 3 Bakugan (one on each card).
3. Tournament mat rules (Toys 'R' Us)
The Tournament mat at Toys 'R' Us has another rule for a miss: the Bakugan that missed goes to the used pile, and then it is the other player's turn. As normal, you can only recycle the used Bakugan once you have run out.
Comment (SG): This provides some additional penalty for missing (using up a Bakugan), but also allows you to recycle your used pile by deliberately missing with Bakugan that you don't want to battle with (although this does give extra rolls to your opponent).
4. Spin Master rules
Spin Master, the creators of the Bakugan game, use a specific rule in-house: "Here at Spinmaster (sic), we usually play by rolling the Bakugan as many times as we wish until it opens."
Comment (SG): Under these rules players will always complete the battles for the two gate cards set after two turns each (fighting on either the second and fourth or third and fourth turns). This makes the rules for winning a card by standing two Bakugan on it (with no other unoccupied gate cards) useless as it can never happen.
In some cases it may be tactically advantageous to deliberately miss. E.g. if you have an ability card with the condition "Play before you roll... If a battle occurs this turn ...", then you may want to let your opponent stand first so that it is possible for there to be a battle after you play the card (although this allows your opponent an extra roll).
Pass rule: Rather than rolling and deliberately missing, a player should be allowed to choose to pass if they wish, and simply not roll. Players may still deliberately miss by rolling, to try and maintain a psychological advantage -- the opponent doesn't know they want to pass -- however if it becomes obvious that both players are continually deliberately missing then the Stalemate rule (below) should apply.
Stalemate rule: Similar to other games (e.g. chess), if both players pass three times in a row then the game is at a stalemate and declared a draw.
An example situation where you do not just gain tactical advantage but actually win or lose the match is if the players are fighting over the last two Gate cards (they already have two each), with no Ability cards left, and both have managed to stand a strong Bakugan on their own opponent's Gate card.
Given the situation, both players can calculate the result of the battle if they stand, based on their opponents G-Power (known -- it is standing open), their strongest remaining Bakugan (known) and their Gate card bonus (known -- if they stand the battle will be on the Gate card where their opponent already has a Bakugan). If both players calculate they will lose the match by successfully standing, then both will choose to pass (deliberately miss) indefinitely and the match is at a stalemate.
With less strict conditions both players may simply strongly believe they will lose the match and the match could be a stalemate (even if they really would have won). E.g. If each player is standing on their own Gate card, then although they don't know for sure the bonuses on their opponent's Gate cards there may be a significant chance they are beneficial for the opponent and not you.