Smith, who was running at the tail end of the field after starting the race in 30th, cut in front of Truex instead of allowing the faster car to go by, breaking an unwritten NASCAR rule.
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Truex, who was in seventh at the time, let Smith know his displeasure with the universal signal for any road-rage incident — his middle finger.
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Truex regained his composure and was among race leaders midway through Sunday’s race.
