Does players speed effect their defense

I have played over 400 games and have noticed that some peoples fielders especially the short stops and outfielders will run down fly ***** faster and better than others at the same level that seem to have the same upgrade level. I also noticed that when I put in my faster players, I give up less runs on defense. Does anybody know for a fact if a players speed does effect their defense or not because I cannot find a for sure answer. If you are only speculating then please don't try to answer this, I only want an answer if you know it as a 100 percent fact. Thanks