In cricket, play usually stops temporarily when spectators or personnel walk or stand in front of the (live) sight screen. What about fielders? Should they move elsewhere on request?
The role of the sight screen is to help the batter see the ball at the start of its flight, as it leaves the bowlers hand. If you think about the angles involved, it is mainly the upper portion of the sight screen that is used, so a fielder standing in front of it would not block this view.
The problem with spectators is typically not that they are in front of the sight screen, but that they are moving in front of the sight screen. Humans are very tuned in to movement visually, so having someone move in the line of sight of the batter is distracting. Under the laws of cricket, fielders are not permitted to move laterally as the bowler is running is (they can move towards or away from the batsmen under Law 41.7, 41.8). Therefore, a fielder in front of the sight screen but stationary will not be distracting the batter. They probably wouldn't notice given that the Umpire and Bowler are also in the way.
Fielding directly in front of the sight screen would be a very poor field placement in any case.
It is not unlawful to field between bowler and side screen. In fact there is a fielding position for that and it is called straight hit.
Usually the fielder is placed at an angle and I don't remember any captains using this fielding position. You can see all the rules here.