In this task, you need to reverse all words of a given length in the sentence. The number of letters in a word determine its length. For example, the length of the word "apple" is 5.
Sentence: 'a woman holds a frisbee close by a second woman that is eying the frisbee with an arm held out while two other players stand waiting in the background'. Reverse all words of length '4' in the given sentence.