Leffler died at Cooper Trauma Center after being extricated from his vehicle and flown by helicopter to the facility, NBC-TV, Philadelphia, reported. He was 37.
He began racing at age 12 and drove the No. 19 Toyota for Humphrey Smith Racing in the NASCAR Sprint Cup Series.
He won four USAC championships and was inducted into the National Midget Auto Racing Hall of Fame in 2003.
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