For position players, the largest point of contention comes in measuring defense and estimating the positional adjustment. Our measures of both are more uncertain than our measures of offense, so players who get a good amount of their value through their defensive ratings likely have more uncertainty around their WAR value than players who have defensive value closer to average. This does not mean that WAR is wrong or biased, but rather that it is not yet capable of perfect accuracy and should be used as such.