how en passent can be legal move in chess

En passant is a legal move as it figures in the Laws of Chess:

'3.7.3.1 A pawn occupying a square on the same rank as and on an adjacent file to an opponent’s pawn which has just advanced two squares in one move from its original square may capture this opponent’s pawn as though the latter had been moved only one square.

3.7.3.2 This capture is only legal on the move following this advance and is called an ‘en passant’ capture.'

It was introduced around the year 1200 when the rules were changed so that a pawn could move 2 squares from its initial position instead of 1 as it was before.

It's there because originally pawns could only move 1 square. En passant allows pawns to maintain that dynamic while speeding the game up.

In the modern day, I think most people find the eccentricity of it endearing.

En passant feels like a ninja move.

Thx guys

The “infield fly rule” of chess, if as comment #3 pointed out if you are going to speed up the game by allowing the pawn to move up two places on it’s first move e.p. Is an option that is reguired. This is why it most be done on the next turn only because a pawn that only moved up 1 square would be allowed to move again and pass the pawn. Also in should be noted that allow e.p. was extensively used it was only codified in the rules in 1880 leading up to a major tournament in Italy.

You didn't have to have the en passant rule to be fair. It was a decision to keep chess semi-consistent with what came before, but that's not neccesary.

e.g. when the Queen was introduced, in theory they could have introduced a rule that said KQ v K is a draw because it was previously a draw by insufficient material when the Queen was a Minister, but they decided not to.

They also could have chosen to have non-pawns capture pawns by en passant, but again chose not to.

What you're going to do to keep in line with the past is a choice.