The legendary Mike Singletary makes his pro football comeback on Sunday when he coaches the Memphis Express against host Birmingham Iron in the new Alliance of American Football league, or AAF. Kickoff from Legion Field is at 4 p.m. ET on the CBS Sports Network. A Hall of Fame linebacker with the Chicago Bears who twice won Defensive Player of the Year ('85, '88), SIngletary went just 18-22 in two-plus seasons as head coach of the NFL's San Francisco 49ers. This is his second chance and he vows to make the most of it. On the opposite sideline will be Iron coach Tim Lewis, a former Green Bay Packers cornerback and 30-year NFL assistant who once served as the Pittsburgh Steelers' defensive coordinator. Sportsbooks list Birmingham as a three-point home favorite, with the over-under for total points set at 47. Before you make any Express vs. Iron picks and AAF predictions, you'll want to hear what SportsLine pro football expert Mike Tierney has to say.

A renowned sportswriter whose work appears in the New York Times and Los Angeles Times, Tierney has reported from seven Super Bowls. He's intimately familiar with all levels of pro football -- including the young, hungry players who populate the AAF -- and knows every coach's philosophy and approach to devising game plans. 

Tierney was all over the Patriots in the 2019 Super Bowl, enabling him to finish the season with a sparkling 63-46 record against the spread. Anyone who has followed him is up big. Now, he's locked in his AAF picks for Express vs. Iron. 

Tierney knows the Iron look loaded on offense with running back Trent Richardson and wideout Quinton Patton boasting significant NFL experience. Just 28 years old, Richardson had a monster rookie season with the Cleveland Browns, amassing 1,317 yards from scrimmage with 12 touchdowns. Patton caught 73 passes for the San Francisco 49ers. 

Luis Perez might not be as well-known as some other AAF quarterbacks, but he could be the best of the bunch. In 2017, he won the Harlan Trophy -- the NCAA Division II equivalent of the Heisman -- after completing 71 percent of his passes with 46 touchdowns. The NFC champion Los Angeles Rams signed him and he spent time on their practice squad last season.

But just because the Iron are stacked offensively doesn't mean they'll cover more than a field goal against Singletary's Express. 

Memphis features two quarterbacks with impressive pedigrees. Hackenburg is a big-armed Penn State product drafted by the Jets in the second round three years ago, while backup Zach Mettenberger started 10 games for the Tennessee Titans in 2014-15. Running back Zac Stacy, 27, piled up 1,114 yards from scrimmage and eight touchdowns in his best NFL season (2013 with Rams). Stacy retired from football in 2015 due to multiple injuries, but returned to the CFL last May. He believes he will be back in the NFL after showing out with the Express. 

It likely will be tough to run on the Express given Greg Gilmore's presence up front. The 6-4, 308-pounder starred at nose tackle for LSU in 2016-17, finishing his college career with 104 tackles, 13 tackles for loss and 10 sacks. 

We can tell you Tierney is leaning Over, but he has found a critical X-factor that makes one side of the spread a must-back. He's only sharing what it is, and who to back, at SportsLine. 

Who wins Express vs. Iron? And what critical X-factor causes one side of the spread to hit hard? Visit SportsLine now to see which side of the Express vs. Iron spread you should be all over, all from the incomparable expert who just racked up another big cash in the Super Bowl.