Is it mandatory to introduce a Second New-Ball in middle of the 50-Over limited One-day cricket match ?(old rule)

Yes, Actually it is one of the new rules which have been introduced in the year 2007.

After completion of 35 overs in a one-day match in both innings it is mandatory and compulsory to introduce a second new ball whether the captains accept it or not. The captain of fielding side is allowed to choose and select any two new cricket balls from the available 12 new balls before actually the innings gets started then accordingly the selected two new balls will be given to the umpires before the innings gets started.

And some of the captains are really not happy with this condition. One of the most important drawbacks of this condition is option of bowling reverse swing and spin bowling will be completely lost and missed.

Because we know that the old ball especially after 35 overs really favors reverse swing bowling which is really important factor for the fielding side captain in the final overs of the match.

In contrast, the new ball really favors the batsman I should say, because the new ball nicely reaches to the batsman after pitching, and moves here and there very fastly, and then outfield will become fast which is very important for the boundaries.

The only favourable factor for the fielding side would be “fielding”, because fielding a new ball would be much easier than fielding a old ball (which might be in out of shape after 35 overs especially in sub-continent conditions).

Before 2007, October, there used to be no any rule of introducing new cricket balls after 35 overs. But there would be some cases like when the ball gets in out of shape especially in Indian-Sub-Continent conditions, and then the umpires would examine the ball, consider it and replace it with old used Cricket balls but not the new Cricket balls.