This is a good position for the captain to be fielding at.
It means they are close to the bowler enabling them to pass on advice and encouragement.
The job of a mid-off fielder is to cut off the straight drive and has to stay on their toes to prevent the quick singles.
There are a couple of different positions in this area:
Mid-off is normally positioned about 25-30 yards from the batsman, while silly mid-off is in close to the batsman looking for bat-pad chances.
Deep mid-off is usually three-quarters of the way from the boundary, while long-off is right out on the rope.
Similar positions on the leg or on side are known as mid-on, deep mid-on etc.