obstruction at first base

[Little Jimmy]

I've been doing a local 11-12 tourney the last few days and was reminded of this. On most balls hit to center or left, F3 runs over and sets up with one foot on first even though there is no play comming her way. Runner is denied inside portion of white bag when rounding 1st and possibly going to 2nd. Anytime I see runner slow or hesitate I throw out the left arm and wait to see what develops ( so far nothing has developed: runner either gets to 2nd easily or hasn't tried but in my judgement never would have made it anyway).

My observation is that I'm also seeing many runners not even attempting to take the inside corner of the white but hitting all orange and swinging wide on their rounding of 1st, essentially taking for granted that F3 can set up on white with no chance at a play. Question: does there need to be some hesitation/contact by the runner to lead to obstruction or can the mere presence of the fielder be enough even if the runner is avoiding her?