It is known as “en passant”. Simple and clear, yet comprehensive commentaries about it will serve as a great explanation. You’ll get the hang of this special move at once.
The essence of the Special Chess move
Today we talk about “en passant”. The phrase came from France, where it means “in passing”. The idea is as follows. One’s piece doesn’t end up on the square of the piece it captured.
How do all captures normally work? Basically, you walk onto the square where the other piece was and then remove it.
But our move is the one exception to that. It’s a special one. Here’s how it is. The rival’s pawn travels two spaces. After that, you attack it with the adjacent pawn as if it was located diagonally.
Now let’s get back in history to understand where this move comes from. Chess used to have a rule that pawns could always move one square only. Nowadays, they can move two spaces, if they’re on the second or the seventh rank. So, earlier in time, pawns would advance slowly towards each other. And then, they’d finally come into contact. One captures the other and the fight begins.
But at some point, people’s attention span seriously decreased. So they decided this is too long to wait to start the battle. And they added the rule that pawns could travel two steps at once.
And here’s an important point. One shouldn’t be able to walk all the way down the board without one thing. This thing is letting the opposing pawn attack. The rival should have a chance to capture the moving piece on its trip. What if they only meet when standing next to each other on the same rank? How’s this pawn supposed to capture the opponent’s one? Legally, it cannot since there’s no such thing for a pawn as moving sideways.
People thought it would mess up the way chess was played too much. So, instead of letting the pawn run past, they created an extra rule. It allowed capturing in passing. When a pawn passes you by, you can attack it. Just move as if it had only gone one step.
This option is only available for one move. You can’t develop other pieces and then suddenly realize you want to attack that pawn with yours. If the rival’s pawn goes past you, there’s just one move window to capture it. And it’s the moment when the pieces stand on the same rank.
Also, it’s important to remember the following conditions. All captures of this sort must occur with a pawn moving from the 2nd rank. And travels to the 4th rank. If a piece comes from the 3d rank, it doesn’t fit the rule. It’s supposed to travel two spaces at once starting from its initial square. Only then can you capture it with this special move.