Foxes are members of the canid family.
Foxes are slightly smaller than coyotes (8-15 pounds) and have long bodies and relatively short legs.

There are five species of foxes in North America, but only two (the red and the gray), are found in urban settings. Interestingly, due to color variations in foxes, gray foxes can look quite red, and red foxes can be gray! 

The most accurate way to tell a red fox from a gray fox is by looking at the tail: red foxes have a white tip at the end of their tail...

Gray foxes can climb trees and do not have a white tip at the end of their tail, despite having some red in other areas of their coat! 

Both foxes are opportunistic and keep caches of food that they bury, much like squirrels do, for times when food is scarce.  
Misunderstanding this behavior has created a myth that they are wasteful killers when in fact, they are creating a natural "pantry" in the ground for later use.

They have adapted to a wide range of habitats and feast on a variety of natural and human-supplied foods. If necessary, they will even adapt their activity periods to times when humans are not active. Despite being one of the most successful urban mammals, many people are surprised to see a fox in their backyard, and that surprise often leads to unnecessary panic. 
(smaller than a basketball or underweight)

(injured or sick)