It's good sportsmanship to not pick up lost golf balls while they are still rolling.
Source: In The Golfer's Book of Wisdom, ed. by Criswell Freeman, 1995.
-- Mark Twain, (Nov 30 1835-1910), US novelist, journalist, river pilot; The Great American humorist was also known as The People's Author and creator of Tom Sawyer and Huck Finn.