In today's Women's US Open semifinal, Caroline Wozniacki won by default after her opponent, Peng Shuai, was forced to retire due to injury. Above, you can see Shuai dropping to the court in pain and being wheeled off.

Peng eventually succumbed to her injury late in the second set of a match she was losing 6-7, 3-4, but the set had earlier been temporarily halted when she complained of leg cramps. At this point it's unclear what the cause of her second injury was—she can be seen clutching at her shoulder and panting. Wozniacki will face Serena Williams in the final.

[CBS Sports]