### Clue: across Jack cut through pegleg, or fixed the 23 problem? (7,6)
### Answer: JOGGER’S NIPPLE 
 ### Explanation: Definition: 23 problem
  J(abbrev. for Jack, as in playing card notation) + [SNIP(to cut) ***contained in***(through)  **anagram of**(fixed)  PEGLEG, OR ]. 
Answer: A 23across(which answer is "running") problem,sore nipples caused byconstant rubbing against the shirt, especially if made of cotton, while running.  To prevent, Wiki advises "run shirtless whenever the law permits".