I’m not sure how you correlate early calls with biased calls but, that being said, you more likely have an umpire getting caught up in the action and letting his anticipation override his tempo. Umpires are trained to hold their calls until the completion of the play. Newer umpires have a tendency to react too quickly and often make their calls before the play is complete leading to the dreaded out-safe-out scenario. Not to say that veteran umpires are immune to hurrying calls but you find it happening less often with seasoned umpires. Just about every one of us has, on occasion , reminded ourselves to Stop-Set-Focus-HOLD then Call after making a call too quickly. It’s not a matter of bias, it’s a matter of poor mechanics.
I was referring to perceived bias, we all know how riled up parents get with "bad" calls against their team, especially if a couple of the calls go against them in succession. When an early call is made it sets up the argument that the umpire already decided to favor the team for which he made the call and no amount of hustle or quality was going to affect the call. The most egregious example of this that I've seen was a girl hustling out of the box, and a shortstop gunning a throw to second, bang-bang could go either way, problem was BU had signaled safe two full steps before the runner had reached first, the defensive parents were irate because of perceived bias. Later BU made a similar call on another bang-bang play at first where he called an out but the 1B in the process of scooping the ball popped it up in from of her and snagged it out of the air, problem was runner's foot hit the bag at the same time the ball made initial contact with the glove, not when it was controlled, the call was in favor of the same team as before. Fortunately he eventually overturned it after discussing with PU. This is where having experienced Umps who know that there is no rush to make a call and allow for the odd bobble, or a quick mental replay really is a wonderful thing. Even in MLB the Umpires have slowed down their calls, probably because they don't want the embarrassment of the play being overturned by replay.