If a player who is signed to an entry-level contract and is 18 or 19 years of age (as of September 15 of the signing year), does not play in a minimum of 10 NHL games (including both regular season and playoffs; AHL games do not count), their contract is considered to ‘slide’, or extend, by one year. For example, if a player signed an ELC for three seasons from 2015-16 to 2017-2018, and their contract slides, their contract is now effective from 2016-17 to 2018-19. An exception to this rule is that if the player is 19 on September 15 of the first year of their contract, and turns 20 between September 16 and December 31, their contract does not slide.
Because signing bonuses are paid regardless of a slide, the bonuses paid on the slide year no longer count to the players remaining cap hit. The cap hit therefore changes - the players salary is averaged without the signing bonus.