The Steam client for Linux now supports using namespaces (a.k.a containers) to run game titles. This feature is available in the latest Steam client beta, and can be used for all native Linux titles in your Steam library. In order to run a title in a container, open the game’s properties dialog, go to the general tab and select ‘Steam Linux Runtime’ under the ‘Force the use of a specific Steam Play compatibility tool’ drop down.
Source: Steam for Linux client adds support for Linux namespaces :: Steam for Linux General Discussions
