So 161 is the score of South Africa . They had lost 6 men getting that score.
That’s why it says 161-6
A team can lose a maximum of 10 players before they stop batting , or when 120 legal deliveries are bowled . Whichever comes first. SA wants the left number to be higher and right to be lower.
India ,batting first scored 176 in 120 deliveries(First innings) . So SA needed 1 more to win the match in the second innings. So 177 to win of 120 deliveries.
At this point SA has consumed 114 deliveries to score 161.
That’s why it says 16 of 6 required. 171 - 161 = 16 runs needed.
120 - 114 = 6 deliveries needed.
If this ball went over the boundary line ,then SA score would be 167 -6 . 10 needed of 5 deliveries with a set batsmen. Very possible.
But due to this unbelievable catch their score is now 161 - 7
They need 16 off 5 deliveries with a new batsman to come out . It’s tough.
The catch itself was insane . In cricket if a ball touches a fielder and the fielder touches the ropes ,it’s considered 6 . So he had to stop the ball and break the contact before his body touches the boundary rope . Due to his momentum ,it was unavoidable to not touch the boundary.
So he broke the contact with ball , then got back into the ground on the other side of the boundary and then re took the catch. This is considered out.