John Gill Commentary 2 Samuel 21:18

"And it came to pass after this, that there was again war with the Philistines at Gob: then Sibbecai the Hushathite slew Saph, who was of the sons of the giant." — 2 Samuel 21:18 (ASV)

And it came to pass after this
After the former battle:

that there was again a battle with the Philistines at Gob ;
in (1 Chronicles 20:4) it is called Gezer; either the place had two names, or these two places were near each other; so that the battle may be said to be fought both at the one and at the other, being fought equally near to both:

then Sibbechai the Hushathite slew Saph, which [was] of the sons of the
giant ;
who is called Sippai, (1 Chronicles 20:4) ; he had his name from the lintel of a door, being as high as one, so tall that he could scarce go under one. Sibbechai was one of David's worthies, (1 Chronicles 11:29) ; perhaps a descendant of Hushah, who sprung from Judah, (1 Chronicles 4:4) .