The total number of points scored by each player throughout a season are listed on a roster by the player's jersey number. is this a function? explain your reasoning.

Yes, this would be a function.

Using ordered pairs to represent this, we would have (jersey #, points).  A relation is a function if no element of the domain matches more than one element of the range; in our case, the domain is the jersey number and the range is the number of points.

The jersey number will not match two numbers of points throughout the season; a player will only have one total number of points throughout the season.  Therefore no element of the domain matches more than one element of the range, and this is a function.