### Clue: Bob upset foreign alto holding one note in essential part of the score (9)
### Answer: OBBLIGATO 
 ### Explanation: Definition: essential part of the score
 **Anagram of**(… upset) BOB + **anagram of**(foreign) ALTO **containing**(holding) [I(Roman numeral for "one") + G(a note in the musical scale) ].
Defn: A musical direction not to omit a certain part of a score during performance.