There is no automatic way to calculate this. But I like the idea and info is also easy to get from the plugin, so I crafted a new shortcode for it: [fp-money-in-the-pot].
You’ll have to wait for the next update to use it, or download the updated class here and replace the file in your install:
/classes/class-football-pool-shortcodes.php
definition:
//[fp-money-in-the-pot]
// Simple shortcode that displays the amount of users in a league (or all users) times a given amount to calculate
// the total sum.
// Can be useful if your players add a stake to the pot and you want to show this number in a post or other part
// of the website.
//
// League can be entered in the following formats:
// league for the user -> league="user"
// league 1 -> league="1"
// leagues 1 to 5 -> league="1-5"
// leagues 1, 3 and 6 -> league="1,3,6"
// leagues 1 to 5 and 10 -> league="1-5,10"
//
// If you omit the league parameter, the shortcode will assume all players in the pool are paying participants.
//
// league : optional collection of league ids, or 'user' for the league of the currently logged on user
// amount : the stake
// format : optional format for the output (uses sprintf notation: https://php.net/sprintf)
examples:
[fp-money-in-the-pot amount="10"]
[fp-money-in-the-pot league="2" amount="7.5" format="€ %.2f"]
small disclaimer: not extensively tested.