The Last Word
The buckler is not a shield that stands in front of the fighter. The buckler is the off-hand's last word — the small round plate of Iron or Steel that rides on the forearm, and the whole argument fits in its size: small enough to be carried, hard enough to be argued with. The fighter who carries a buckler is already carrying a sword, and the buckler is what the sword's hand gives the other hand in return.
A common buckler is a plate of iron, the width of two palms, set with a single rivet and a strap. It takes the blow into the rivet and the rivet into the arm. A master buckler is a plate of steel, and the steel is the part that takes the edge of the edge — the buckler does not stop the sword, the buckler meets the sword, and the meeting is the argument. A masterwork buckler is a story event, and the story has not written it yet, because the buckler is not the kind of work a story keeps.
In the Hand
The buckler is the second stance, made small: meet. The off-hand brings the plate into the blade's line, and the sword's hand takes what is left. The fighter behind the buckler is faster than the fighter behind the kite, and pays for it with the rivet. The buckler is not the line. The buckler is the counter-argument, and the counter-argument is the one the off-hand keeps.
"A buckler is a sentence with one word in it. One word is enough, if the word is hard." — Tigole