Possible Clues:

• Uncompromising backing for club perhaps, when it's entered
• Having a violent effect
• It's back in character, turning savage
• Forceful eccentric securing its retreat
• Doctor attending when spasm's serious
• Chief among detectives turned desperate
• Far-reaching
• Grave produced using spade, perhaps, covering its back
• Severe measure, we hear, to bring old Mexican to doctor
• Extreme — forceful