Second middling mark given to female (weight set back movement) (7)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

S(abbrev. for “second” in time notation) + C(the grade given in a test that signifies average performance/middling mark given) plus ( to ) HER(third person pronoun for a female) + reversal of ( … set back ) OZ(abbrev. for for “ounce”, a unit of weight). Defn: … in a symphony or sonata.