Call to Arms
From Destinypedia, the Destiny wiki
Players must complete Crucible matches. A single completed match grants 15% towards the goal, with a bonus for kills and assists; an average match should net between 20 and 30%. Completing the Call to Arms rewards one Luminous Engram, which can drop Nightfall-quality loot. Players on Xbox One will complete an achievement if Call to Arms is completed.
The PvE equivalent of this activity is the weekly Flashpoint.
Destiny 2 update 1.0.3 altered the amount of Crucible matches necessary to complete the Call to Arms. Originally, every win granted 10% towards the goal, and every loss granted 7%. Player participation, measured by kills and assists, could boost that percentage slightly. In all, an average match would net around 10%, though it was possible to complete the Call to Arms in fewer than 10 matches.