MLB Draft 2013: Mark Appel already has his Astros rookie card - The Crawfish Boxes
Oakland A's news: Phillies' Mark Appel gets first MLB callup at 30 - Athletics Nation
How the Houston Astros Revolutionized Player Development - The Ringer
Astros: Revisiting the 2013 amateur draft hits, misses
Faith, family help Astros prospect Appel endure early struggles
Appel recovers from harsh greeting to pro ball
2013 MLB Redraft: Astros land Judge
Top overall pick Mark Appel signs with Astros
Appel, Despite Potential, May Fall in Baseball Draft Again - The New York Times
Phillies call up former No. 1 pick Mark Appel to active roster – Philly Sports
Did Padres whiff on Mark Appel? - The San Diego Union-Tribune
Remembering a rare draft mistake from the Astros' dynastic era
Astros welcome No. 1 pick Appel to the family
Former No. 1 pick Mark Appel makes MLB debut nine years after being drafted, Sports
Astros To Sign Mark Appel - MLB Trade Rumors