A football player is moving southward and suddenly turns eastward with the same speed to avoid an opponent. The force that acts on the player while turning is

Initial velocity along south   $(-\hat{j})$
Final velocity along east  $\left(\hat{i}\right)$
Change in velocity =$(\hat{\mathrm{i}}-(-\hat{\mathrm{j}}\left)\right)=\hat{\mathrm{i}}+\hat{\mathrm{j}}$
So, acceleration or force is along $\hat{i}+\hat{j}$  direction.
Hence, the force acts along north–east direction.