In typical Gladwell fashion, the author draws from disparate examples to illustrate research that shows how weaker opponents in any contest, from sports to war, often find a way to come out on top. He finds that successful underdogs adopt tactics of insurgencies: attacking where opponents are weakest, challenging the established rules and common mindset. They use speed to their advantage, keep moving and are relentless.
Gladwell tells the remarkable story about a novice girls basketball team in California, coached by a software engineer from India, who made it all the way to the U.S. national championships. Six of the girls had never played basketball before. The coach used a full-court press and some nifty logic to successfully challenge the conventional approach to the way the game is played.
He also examines the tactics of an obscure British archaeologist who in the First World War led bands of Bedouins in the desert to a series of improbable victories against the Ottoman Army occupying the Middle East. T.E. Lawrence's exploits against long odds earned him the title "Lawrence of Arabia." Like David beating Goliath, the underdog can often win by substituting hard work and cunning for ability.
You can read Gladwell's examination of these traits in his piece, "How David Beats Goliath."
For a scene from David Lean's famous movie about Lawrence of Arabia, see this link that illustrates how Lawrence (played by Peter O'Toole) planned to attack the coastal town of Aqaba.