In order to win, you need to earn all four of your Arrow Pieces by exchanging a certain amount of points for each one (usually 50, 75, or 100 each; it depends on how long you want the game to last). There is one complete set of Arrow Pieces for each player. To earn points, you have to use your other cards to attack and earn yourself points (covered in part 4). Arrow Pieces are unique cards that you place next to your deck until you're able to claim them. They look like this...
When you have enough points, during your turn you can choose to trade in those points, select one Arrow Piece, and place it somewhere on your grid. All of them boost certain stats slightly for the card they're pointing to. When somebody earns their fourth one, the game ends instantly.
I know this sort of sounds like the prizes from the Pokemon trading card game, but this is where the similarities end. When you place an Arrow Piece on your grid, it is stuck there. It cannot be removed from the field, and it can't be moved (unless you have certain cards that move others). Because it can't defend against attacks at all, it allows enemy attacks to go right through them, allowing them to score.
There's no room to protect the player from an attack that lets the opponent gain 11 points. The only choice is to destroy that field card quickly!
The opponent has used your own Arrow Piece to protect his own card. It is completely vulnerable from the front, but the Down Arrow Piece is stuck in that spot. You can't attack it from the front. This is why he placed the Field card in the center.
So, you can see that when you're winning, meaning you have more Arrow Pieces than your opponent, it gives them more chances to break through and catch up. However, why not just amass enough points to get all four Arrow Pieces at once, then? I caught this very early on and dealt with it pretty simply. You can only exchange for an Arrow Piece once per turn. Those extra turns in which you're trying to claim the other pieces can cost you in a close battle. Also, I purposely created quite a few cards that discourage getting tons of points; several cards steal a percentage of points or cut the opponent's score in half, or do similar effects. There's also one card whose attack power is the same as your opponent's current score, and can be extremely lethal if somebody tries storing a ton of points.