England have qualified for the T20 World Cup semi-finals following a convincing win over USA. The clash between South Africa and West Indies is now a virtual quarter-final - but England will still be watching the game keenly, with net run rate at play.

England have four points, with victories over West Indies and USA and a defeat to South Africa. The Proteas already have four points, and it is possible for West Indies to finish on four points as well, if they beat South Africa. However, England have ensured that, in case of a three-way tie, their net run rate will stay ahead of South Africa’s, whose two Super Eights victories against USA and England have come by narrow margins.

For South Africa, therefore, the equation is simple. Avoid defeat, and they will top the group. Lose, and they will be out, despite winning their first six games in the competition.

In the case of a West Indies win, the winner of the group will be decided by net run rate. West Indies are currently placed on a healthy 1.814, but England are marginally ahead on 1.992. However, West Indies will need a significant margin of victory to overtake England - it is possible for them to lose and for their net run rate to dip.

Assuming a full 20-over game, West Indies would need to win by somewhere in the region of 30-50 runs if batting first, with the margin needed smaller the more runs West Indies score. Should they make 250, they would need to win by 32 runs. Should they make 125, they would need to win by 50 runs.

If chasing, again the margin changes depending on the exact scores involved. If chasing 125, they would need to reach the target inside 15.3 overs. If chasing 250, they would need to reach the target inside 17.4 overs. West Indies can also give an extra boost while chasing by reaching the winning total with a boundary, and thus clearing South Africa’s score by more than one run. Roughly, each extra run scored gives them another ball to play with to overtake England.

Why could top spot be important? The winner of each group plays the second-placed team in the other. India are well-placed to top group two, with Afghanistan or Australia poised to take second place. Given India’s form, teams may want to avoid them until the final, if possible.

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