One of the primary crib points in the teams that I have worked with was linked to rewards and recognition. While rewards that have a link to performance (and is measured) were easy to award as the number did the speaking, in many cases, employee behaviours that led to wins were open to subjective review, and here the training as well as quality of managers came into play. The better ones always ensured that the good deed of the employee was recognised, while the others often ignored the act as they were too busy fighting fires or getting their basics right.
In such a scenario, to fix the issue I implemented self nomination, which received its fair share of pushback but proved to be an excellent solution to curb the disgruntlement amongst employees. Any employee who felt that they had done something that deserved an award or a mention in a formal forum was invited to update a form (self nomination) which once submitted was routed to an independent awards committee, made up of employees across all bands and levels in the organisation(sans the leadership team). This committee reviewed all nominations and approved or rejected the same, all rejections updated with a complete justification (which was also open to appeal).
This transparent and unique process brought an end to all grievances, and never again did I hear of awards being biased or dependent on the line manager.