There are only two references to him. Judges 5:6 tells us that he lived at the time of Deborah during a period when Israel was in a weak position and her enemies had confiscated all the weapons in the land. "War came to the city gates and not a shield or a spear was seen among forty thousand in Israel ."
This however did not deter Shamgar. With the spirit of the British Home Guard in WW2, he used what he had to hand and turned it into a weapon to defend his home and family. Chapter 3:31 says Shamgar struck down 600 Philistines with an ox-goad. An ox goad was a strong pole, about 8ft long with a sharp metal prod at one end and a spade at the other for cleaning dirt off a plough.
Warren Wiersbe says, "Instead of complaining about not possessing a sword or spear Shamgar gave what he had to the Lord and the Lord used it. Joseph Parker said, " What is a feeble instrument in the hands of one man is a mighty instrument in the hands of another, simply because the spirit of that other burns with holy determination to accomplish the work that has to be done."
There are a lot of excuses made among God's people that they cannot do the work for God they want to do because they don't have the resources of people, money, buildings, technology, talent or experience and they give up. Now there certainly should have been some questions asked as to why the people of God had got themselves into the position where their enemies had so much control over them. Judges 5:8 tells us that the situation arose because of idol worship among the people "When they chose new gods war came to the city gates." It is important to examine the reasons for lack of success and oppression of God's people by the world around it. But I also thank God for faithful people who carry on fighting whilst others have given up and investigations is taking place. For example, I got saved as a child, despite the fact that there was not widescale revival where I lived and at a time when the Church in the UK was declining rapidly. How did that happen? People around me didn't give up, they used what they had to hand to teach and preach the gospel.
And whilst Shamgar held on and fought with what he had, at the same time God was raising up Deborah, who did not just hold on but took back what the enemy had stolen.
Keep fighting and keep on believing for greater things.