Straddling the foul line

[scarolinablue]

Playoff time. Moving to 3-man and 4-man crews. There was a discussion amongst a few of us in our association as to whether it is an acceptable mechanic for the U1 or U3, when on the line and a runner on their respective base, to straddle the foul line. The main arguments for were to provide a slightly better angle for either a check-swing or pick-off throw to the base. The main arguments against were that you should just never straddle the line.

Some were certain they've seen this done at higher levels of ball (i.e. minors and MLB). Being that this is FED ball we're talking about, is this an acceptable mechanic? If so, under what conditions?