Please give feedback on this script

Your code is clear and easy to follow. It has meaningful variable names. As long as you get at least one player name and valid input, your code will be fine.

splayers = '' is declared near the beginning of your code, but you never use its value. It can be safely removed.

If the user's first input is n, then no players are added to the players list. This is not a problem until you do players[keeper-1], which, for any int value of keeper, will give you an IndexError: list index out of range.

If your user's input is yes, the value of ask.lower() == 'y': will be False. This may or may not be what you intended. You could use ask.lower().startswith(), or you could assume your users will follow directions and just type y or Y.

You could change your for loop to

for index, player in enumerate(players, 1):
    print(f'Player {index}: {player}')

F-strings are another way of formatting strings, and may be faster than using .format. Python for loops tend to be of the form for player in players: to get at the items directly, and switch to using for item, index in enumerate(players): if they need index numbers. Using enumerate(players, 1) will start the index counter at 1.

What do you want to happen if the user doesn't type something that can be parsed as in int to your keeper variable? Right now, you get a ValueError: invalid literal for int() with base 10. You could use

try:
    keeper = int(input('\nPlease select the goal keeper by selecting the player number. (1-{})  '.format(len(players))))
    print('\nGreat!! The goal keeper for the game will be {}.'.format(players[keeper-1]))
except ValueError:
    pass;

The length of the string keeper = int(input('\nPlease select the goal keeper by selecting the player number. (1-{}) '.format(len(players)))) is 115 characters, and print('\nGreat!! The goal keeper for the game will be {}.'.format(players[keeper-1])) is 84 characters. You might want to keep your lines at a maximum of 80 characters to increase readability.

I would not necessarily make ask = input('Would you like to add a player to the list? (Y/N) ') into a function, but I might want to have 'Would you like to add a player to the list? (Y/N) ' stored in a variable as to not need to retype it and have consistent spelling. You don't have spelling errors, but the more you type something out, the more likely it is that you will misspell something, and if you want to change the prompt, you would only have to change it in one place.