Travel rules apply any time that a player takes possession of the disc, not just after a catch.
An offensive player may be as close as possible in front of or to the side of a stationary defender if contact is not made. This is not a pick, as the defender can avoid the offensive player.
An offensive player must allow a defender space to take a reasonable step backwards without contact, or it is a pick.
If both the offensive player and the obstructing player are making a play on the disc in the air, then it is not a pick.
On a pick, advantage applies if the disc is in the air or if the thrower is in a throwing motion; advantage does not apply if the disc is not in the air and the thrower is not in a throwing motion. Referees should immediately whistle if there is no advantage and delay the whistle if advantage applies.