Tightly grasp (6)
(Other definitions for clutch that I've seen before include "Grasp - eggs - car pedal" , "Hold the car mechanism tight" , "Handbag" , "Grasp, hold firmly" , "Grip part of the car-engine" .)
(Other definitions for clench that I've seen before include "Close teeth or fingers tightly" , "Sharply contract (muscle)" , "Hold in a tight grasp" , "Squeeze together tightly" , "Close, grasp, tightly" .)