Clarification on using ^ and $.

You may have discovered a bug in the challenge checker (I'm checking with Kenneth). Meanwhile....

A search pattern stops and returns a value as soon as it matches. The use of a caret (^) or dollar sign ($) signify that the matching text must include the start or end (or both) of the line. Note that, by default, the pattern matching is "greedy", in that, it will consume as many characters as it can while matching. This is why "+" for "one or more" gets the whole word or whole numeric group. At play in this pattern is the use of question mark (?) which signifies "zero or more" of the previous character or group.

By ending the pattern with "?", it says that the score field is optional. It also makes the comma between the last_name and first_name optional and a comma or colon between the first_name and the score field optional. Thus the "NOT USED" pattern

import re

string = '''Love, Kenneth: 20
Chalkley, Andrew: 25
McFarland, Dave: 10
Kesten, Joy: 22
Stewart Pinchback, Pinckney Benton: 18'''

players = re.search(r'''
    (?P<last_name>[\w]+),?\s
    (?P<first_name>[\w]+)[,:]?\s
    (?P<score>[\d]+)?    #  $ NOT USED
    ''',string, re.X | re.M)

matches and returns the false positive result:

('Stewart', 'Pinchback', '') with empty score field.

By adding the end-of-line anchor "$" makes the EOL required which forces the score field to be used in order to reach the EOL character. Note that by removing the last "?" also makes the score field required.

Possible bug: Using the EOL anchor passes the challenge, but also returns the false positive result

('Pinckney', 'Benton', '18')

I'm checking with Kenneth on that.

Using many optional elements can make it difficult to see all of the optional false positive matches.

One way to eliminate using "?" for optional fields is to expand the first_name and last_name groups to allow for the optional SPACE:

# This passes the challenge
players = re.search(r'''
    (?P<last_name>[\w ]+),\s  # optional space in last_name. comma now required
    (?P<first_name>[\w ]+):\s  # optional space in first_name, colon required
    (?P<score>[\d]+)    # score required Note "used" or "not used" '$' does not matter for this pattern
    ''', string, re.X | re.M)

Eliminating optional fields makes the pattern much easier to read and absorb the intent