A FASTBALL, in slang, is a type of pitch thrown by a pitcher in baseball. The term 'FASTBALL' can be broken down into three crossword solutions: HEAT (4 letters), CHEESE (6 letters), and HEATER (6 letters). HEAT is a reference to the speed of the pitch, as it is thrown with great velocity. CHEESE is a reference to the ball's movement, as it moves quickly and unpredictably. Finally, HEATER is another term for a FASTBALL, as it is thrown with a lot of HEAT.