2 Samuel 21:15 Once again there was a battle between the Philistines and Israel. David went down with his men to fight against the Philistines, and he became exhausted. 16 And Ishbi-Benob, one of the descendants of Rapha, whose bronze spearhead weighed three hundred shekels(b) and who was armed with a new sword, said he would kill David. 17 But Abishai son of Zeruiah came to David’s rescue; he struck the Philistine down and killed him. Then David’s men swore to him, saying, “Never again will you go out with us to battle, so that the lamp of Israel will not be extinguished.”

18 In the course of time, there was another battle with the Philistines, at Gob. At that time Sibbekai the Hushathite killed Saph, one of the descendants of Rapha.

19 In another battle with the Philistines at Gob, Elhanan son of Jair[c] the Bethlehemite killed the brother of[d] Goliath the Gittite, who had a spear with a shaft like a weaver’s rod.

20 In still another battle, which took place at Gath, there was a huge man with six fingers on each hand and six toes on each foot—twenty-four in all. He also was descended from Rapha. 21 When he taunted Israel, Jonathan son of Shimeah, David’s brother, killed him.

22 These four were descendants of Rapha in Gath, and they fell at the hands of David and his men.

b. 2 Samuel 21:16 That is, about 7 1/2 pounds or about 3.5 kilograms
c. 2 Samuel 21:19 See 1 Chron. 20:5; Hebrew Jaare-Oregim.
d. 2 Samuel 21:19 See 1 Chron. 20:5; Hebrew does not have the brother of.

This is from Bibletrack.org.

When they go out to fight the Philistines, Abishai has to bail David out from apparent death from a giant Philistine warrior named Ishbibenob. Because David just isn't the warrior he was in his youth, his men decide he just isn't battle worthy any longer. Then David's army fought a series of battles with the Philistines - winning each one. The really big Philistine with the unusual hands and feet is given special mention here - he had six digits on each hand and foot. I'm not sure how that enhanced his battle abilities, but after David's nephew (Jonathan the son of Shimea the brother of David) took out this Philistine giant, it must have made quite a conversation piece. Altogether, we have the slaying of four giants in this passage - warriors for the Philistines.

This is from Bible.org.

The next paragraph, verses 18-22, follows closely on the heels of verses 15-17. In the former battle with the Philistines, David had been attacked by one of Goliath's offspring and had nearly been killed. The decision was reached that David would no longer accompany his men in battle. But could they win without this Goliath-killer? Was David essential to Israel's victory against the Philistines? Verses 18-22 give us the answer. In subsequent battles, other descendants of Goliath emerged, and they were killed also. There was Saph, who was struck down by Sibbecai the Hushathite (verse 18). Then in a battle at Gob, Elhanan the son of Jaare-oregim the Bethlehemite killed Goliath the Gittite (verse 19).

The final “Goliath” descendant is saved until last, and no wonder. This fellow not only intimidated his opponents by his size but by his extremities. Can you imagine this fellow being an offensive lineman for the Denver Broncos, and you being his counterpart on the defensive line? You are both down in your stance, ready for the ball to be hiked. You look down at the ground and notice his hands. You start counting his fingers . . . one . . . two . . . three . . . four . . . five . . . . . . . . . . six? Then you look at his other hand, and then his feet. What a sight he must have been! Nevertheless, Jonathan the son of Shimei, David's brother, struck this giant down like the rest. He did not fall on all 4's; he fell on all 24's. Whether by the hand of David or by one of his men, they all fell to the army of Israel.

Well, it's been a bloody fight with the Philistines [nowadays Palestinians] and their giant soldiers have fallen. Since David took on Goliath, the Israeli soldiers aren't intimidated by them any more. As a matter of fact.... David doesn't have to be there to win the battle.