Matthew Poole and continuators on Judges 20:30

30 And the children of Israel went up against the children of Benjamin on the third day , and put themselves in aray against Gibeah, as at other times.

i. e. A considerable part of them, who were ordered to give the first onset, and then to counterfeit flight, to draw the Benjamites forth of their strong hold. See v. 32.

To wit, after the second Battel; for the first day after it, they spent in perplexing thoughts, and going up to the House of the Lord: the second, in Fasting and Prayer there: and this third, in the Fight. Or, this is so called with respect unto the two several foregoing days of Battel, and so this was the third day of Battel.