Question: When 4 clubs are involved, what is the average number of fixtures?
SQL: SELECT AVG("Fixtures") FROM "2-10287593-1" WHERE "Clubs involved" = 4.0;

Question: In the sixth round, what is the sum of fixtures when there were more than 15 clubs involved?
SQL: SELECT SUM("Fixtures") FROM "2-10287593-1" WHERE "Round" = 'sixth round' AND "Clubs involved" > 15.0;