What is pickup soccer? or pick-up soccer? or whatever?
Pickup soccer is an informal gathering of people that play soccer. It is comparable to pickup basketball, softball, or any other pickup sport, but it seems as though soccer usually requires a bit more organizing - either because people like to have more than a couple of players to play a game, or because grass fields are tough to come by - especially in urban areas, etc. Dictionary.com defines the word 'pickup' as: Being, relating to, or involving a group of people assembled informally for a temporary purpose: [a pickup orchestra; a pickup baseball game].

http://www.socster.com/help.php

Судя по описанию, приведенному в разных источниках, это любительская встреча в свободное время людей с разным уровнем подготовки или вообще без какой-либо подготовки.