The question is did Williams do a) or b) ?
a) Initiating contact with an opponent by shoving or pushing off, thus creating a separation in an attempt to catch a pass.
b) Contact by a player who has gained position on an opponent in an attempt to catch the ball.
a is illegal, b is not . I think if the Eagles player is tighter to start this does not get called, but because the defender is carrying so much momentum that get stopped/slowed by Williams, who already gained position, it looked like a push off. I think this one could of gone either way. If Williams just goes up for it and draws contact it might even be called the other way, but he was flat footed reading the ball with a guy running towards him, it's kind of a natural reaction to put your arm out to protect yourself and absorb that player coming into your space.
The calls on the Dez passes are more illegal contact, although Dez basically tries to run through people. I think that contact happens on 80% of plays in the NFL but Dez forces a call because the defender is impeding him . The question becomes are is Dez trying to evade him and did he release contact after 5 yards. Then when the ball is in the air did he try to play through Dez's back or prevent Dez from turning in any way.
ARTICLE 2. ILLEGAL CONTACT WITHIN FIVE YARDS. Within the five-yard zone, if the player who receives the snap remains in the pocket with the ball, a defender may not make original contact in the back of a receiver, nor may he maintain contact after the receiver has moved beyond a point that is even with the defender. Note: If a defender contacts a receiver within the five-yard zone of the line of scrimmage, loses contact, and then contacts him again within the five-yard zone, it is a foul for illegal contact. ARTICLE 3. ILLEGAL CONTACT BEYOND FIVE-YARD ZONE. Beyond the five-yard zone, if the player who receives the snap remains in the pocket with the ball, a defender cannot initiate contact with a receiver who is attempting to evade him. A defender may use his hands or arms only to defend or protect himself against impending contact caused by a receiver. Note: If a defender contacts a receiver within the five-yard zone and maintains contact with him, he must release the receiver as they exit the five-yard zone. If the defender maintains contact beyond five yards, it is illegal contact.