Subsequent award of penalty runs affecting right to enforce follow-on
What should happen if;
(a) the side batting first does not have sufficient lead to enforce the follow-on but subsequently penalty runs are added to its score bringing it up to the required total?
(b) the side batting first enforces the follow-on and subsequently penalty runs are awarded to the other side, reducing the difference between the sides’ scores to less than the level required for the follow-on?
Neither situation can arise. The follow-on is not an issue until both sides (A first, then B) have batted. Then, if it does not have the requisite lead, side A will have to bat again. Any penalty runs awarded to side A now will be added to its score in this, its second innings. If penalty runs are awarded to side B they will be added to their first innings total, increasing it beyond the number which was already too large for side A to make them bat again.
If side A does enforce the follow on, then side B bats next, after having just batted. Any penalty runs acquired now will be added to its current innings not to its first one. If side A is awarded penalty runs, they will be added to its first innings total. They already had sufficient lead for the follow-on, and the extra runs only increase that lead.
[Law reference: 13.1, 42.17(d)]