Spotting Assist is a credit for the act of targeting an enemy 'Mech when a teammate successfully attacks it with indirect missile fire (i.e., LRMs). The criteria for getting the credit is that you are the first to target the enemy 'Mech, be in line-of-sight of the 'Mech and within sensor range and the 'Mech must be hit by a teammate's LRMs during that target lock. A credit can be achieved once per target for each teammate that successfully strikes the opposing 'Mech with your assistance.[1][2]
You will be awarded 2,000 c-bills and 20 XP for each act of spotting assist.[3]