there is no such thing as ''hiding the ball''
look at arm swing like Ben Sheet, Madison Bumgarner , Derek Holland , andy sonnanstine, Chad Billingsley etc
their arm swing is just swing too much, which means they start towrads their back, as a result, the hitters can see the ball
like this pitcher illustrate here
this may create more pressure on their shoulder, thats why those pitchers who have this kind of arm swing, tend to have shoulder injury!!!!!
if your arm swing is pendulum swing but did not swing towards your back,
like Jon Lester,
Roger Clemens (Red Sox and new york yankee) ,
Roy halladay (earlier age with overhand release point) ,
Greg Maddux, justin Verlander,
Alfredo Figaro (Tigers pitchers in 2010, im not sure where is he now), Johney Cueto,
Tim Lincecum , Roy Oswalt, Andy Pettite etc
when their pitching hand is vertical usually its behind the head, so standing from hitting stance of view, of course you can not see the ball, until it release
because they start their arm swing, from side body , instead towards their back, and this type of arm swing is also what i recommand and suggest to most of people if your arm swing is pendulum swing type.
like those pictures here
there are some pitchers with the arm swing, is to left up the elbow first, and some of them , when the pitching hand is vertical, the ball is not behind their head, its behind their ear so the hitters can see the ball as well
like Johan Santana, A.J Burnett, Stephen Strasburg etc
some scouting report will say
''they have timing problem '' because when the pitching is vertical, its not behind their head.