Possible Clues:

• I'm starting to be one foot long.
• With this foot, one goes to a doctor
• Foot trapped between taxi and ambulance?
• Foot injury initially requires a doctor
• Metrical foot of two syllables
• William Booth took part in 17
• I'm beginning to be short and long by the foot
• Poetic element in full version of Billy Budd?
• A fragment from William Blake?
• Metrical foot of one short, one long syllables