The follow-on rule is basically used to enforce a batting team’s second innings immediately after their first innings in Test cricket if they fail to score a minimum threshold in comparison to the opponent’s first innings total.
The follow-on is applied in matches spanning five days or more. If Team A bats first and posts a significant total, Team B must score within 200 runs of Team A’s total to avoid the follow-on.

For instance, if Team A scores 500, Team B must score at least 301 to make Team A bat again. If they score 300 or fewer, Team A’s captain can opt to enforce the follow-on.
This rule is governed by Law 14 of the MCC Laws of Cricket:
14.1 Lead on first innings
14.1.1 In a two-innings match of 5 days or more, the side which bats first and leads by at least 200 runs shall have the option of requiring the other side to follow their innings.
14.1.2 The same option shall be available in two-innings matches of shorter duration with the minimum leads as follows:

14.2 Notification
A captain shall notify the opposing captain and the umpires of his/her intention to take up this option. Once notified, the decision cannot be changed.
By enforcing the follow-on, Team A makes Team B bat their second innings immediately, skipping Team A’s second innings. This strategy is often employed when time is limited or when the pitch is deteriorating, giving Team A a better chance of winning.
The decision to enforce the follow-on rests solely with the fielding captain, making it a strategic choice based on match conditions.
In the third Test against Australia in Brisbane on Tuesday, the final wicket partnership between Jasprit Bumrah and Akash Deep proved crucial on Day 4, helping India avoid the follow-on and reach 252/9 in 74.5 overs at stumps.
India faced a challenging situation in the last session after Ravindra Jadeja’s dismissal for 77, with the team still needing 33 runs to avoid the follow-on.
Akash joined Bumrah at the crease, and together they constructed an invaluable unbeaten 39-run stand from 51 deliveries, causing frustration for the Australian side on a day affected by rain.

At the close of play, which came early due to poor light, Akash remained not out on 27 from 31 balls, while Bumrah was unbeaten on 10. India still trail Australia’s first innings total of 445 by 193 runs, with Wednesday’s weather conditions likely to influence the match outcome.