Charles Ellicott Commentary John 19:31

"The Jews therefore, because it was the Preparation, that the bodies should not remain on the cross upon the sabbath (for the day of that sabbath was a high [day]), asked of Pilate that their legs might be broken, and [that] they might be taken away." — John 19:31 (ASV)

The account of the piercing of the side (John 19:31–37) is peculiar to St. John.

The preparation, ... an high day.—Compare Excursus F: The Day of the Crucifixion of our Lord, p. 559. The Roman custom was to allow the bodies to remain on the cross. To the Jews this was defilement (Deuteronomy 21:22–23), against which they were the more anxious to take precaution because the approaching Sabbath was an high day.

That their legs might be broken.—The breaking of the legs by means of clubs was a Roman punishment, known by the name of crurifragium, which sometimes accompanied crucifixion, and appears also to have been used as a separate punishment. It is not otherwise clear that its purpose was, or that its effect would be, to cause death, but this is the impression we derive from the present context (John 19:33).