John Gill Commentary Judges 1:20

"And they gave Hebron unto Caleb, as Moses had spoken: and he drove out thence the three sons of Anak." — Judges 1:20 (ASV)

And they gave Hebron unto Caleb, as Moses said
Which was done in the times of Joshua, both by him and all the people, according to the order of Moses. This is to be understood not of the city which was given to the Levites, but of the fields and parts adjacent, (Joshua 14:13) (Joshua 21:11Joshua 21:12) ;

and he expelled thence the three sons of Anak :
whose names are given (Judges 1:10) ; this shows that this refers to the same expedition as in (Joshua 15:14) ; and is expressed in the same manner.