Say, there is a no ball in the very first ball of an innings. Total score becomes 1, over 0.0 What should be the current run rate at this moment ?
Run rate is defined as runs / (legal deliveries * 6) - i.e. runs per over. As the number of legal deliveries is zero, the current run rate is undefined. This is just the same as (e.g.) how a batsman's average is undefined if they have played only one innings and were not out - but frankly, it doesn't matter because everything fixes itself once a legal delivery occurs.