As best I can find, the 4 motorsports accidents that killed more than 10 people:

4-(11)-1957 Mille Miglia-Driver Alfonzo de Portago, his navigator and 9 spectators
3-(11)-2011 Reno Air Races-Pilot James Leeward and 10 spectators
2-(16)-1961 Italian Grand Prix-Driver Wolfgang von Trips and 15 spectators
1-(84)-1955 Le Mans 24 Hour-Driver Pierre Lavegh and 83 spectators