Possible Clues:

• Runner's more pleased with himself when crossing line?
• Criminal, vacant setter admits J K Rowling's human
• He does his running on the quiet
• Exciseman's foe
• One who ignores his customary duties
• He tries to evade customs barriers
• Transporter of illegal goods
• Runner more self-satisfied crossing line
• Criminal speller initially, one unable to spell right
• Runner more complacent when crossing line