  Blockchains have witnessed widespread adoption in the past decade in various
fields. The growing demand makes their scalability and sustainability
challenges more evident than ever. As a result, more and more blockchains have
begun to adopt proof-of-stake (PoS) consensus protocols to address those
challenges. One of the fundamental characteristics of any blockchain technology
is its crypto-economics and incentives. Lately, each PoS blockchain has
designed a unique reward mechanism, yet, many of them are prone to free-rider
and nothing-at-stake problems. To better understand the ad-hoc design of reward
mechanisms, in this paper, we develop a reward mechanism framework that could
apply to many PoS blockchains. We formulate the block validation game wherein
the rewards are distributed for validating the blocks correctly. Using
evolutionary game theory, we analyze how the participants' behaviour could
potentially evolve with the reward mechanism. Also, penalties are found to play
a central role in maintaining the integrity of blockchains.
