Analyzing Marlins waiver claims John McMillon and Brett de Geus

After being designated for assignment by their previous teams, John McMillon and Brett de Geus have been claimed by the Marlins in recent days. Both have been optioned to Triple-A Jacksonville. Although we aren't going to see them in the big leagues immediately, they have the potential to make a positive impact in the near future as pieces of this new-look bullpen. I am going to break down why the Marlins may have been interested in these players, or what I believe they may look to tweak. 

McMillon broke out onto the scene last year, striking out every batter in sight and making his MLB debut with the Royals. During his short spurt in the big leagues, he posted impressive numbers. 

McMillon was ranked 17th among Royals prospects coming into the season, according to MLB Pipeline. Why would the Royals get rid of a reliever who was viewed so highly and also has all three of his minor league options left? The answer is he has struggled commanding the baseball in 2024 and has had an unusual velocity decrease, although his slider is still as elite as ever.  

McMillon is the classic high-velocity bullpen arm. Even with a decrease in both his pitches, he is throwing his fastball at 95 mph this season in AAA and his slider at 84 mph. Last season between AAA and MLB, he threw his fastball at 99 mph and his slider at 86 mph. This is unusual, but potentially fixable. His velocity has gradually increased as his arm slot and release point fall back in line with his career norms. 

A major change McMillon has made in the past two months is upping his slider usage. 

To highlight just how good his slider is, last season in his brief MLB stint, he got 75% whiff on it. Relying on his slider may be the way to go especially with shaky control and a fastball that even when in the high 90s doesn't miss many bats. This season in the minor leagues, McMillon has thrown his fastball for a ball 47% of the time. This is extremely poor, and as a result, many hitters may be sitting on his slider. 

McMillon's fastball has been hit hard in all parts of the strike zone. He has a poor VAA along with 15 inches of IVB, which grades out as a below-average fastball even with elite velo on it. The Marlins could look to take a page out of the Red Sox playbook and continue to lower usage of a poorly graded fastball and up the slider usage even more, or develop a sinker that would play more efficiently off of his slider, allowing him to attack righties inside.

His fastball comes in with -4.9 VAA, which would be 12th percentile in MLB—this means he should be attacking players higher in the zone with the fastball. He does this, but it is still being hit hard. Maybe hitters are able to pick up the difference between a high fastball and a low slider easily so they can sit on a pitch, or it could be the shaky control. 

Overall, the Marlins claimed a guy in McMillon who with some tweaks, may have the upside to be a high-leverage arm. 

Now Brett de Geus is the opposite type of pitcher. A journeyman right-hander who was most recently with the Mariners org, de Geus brings an unorthodox arm movement and a unique pitch mix. Can he find a home here in Miami?

de Geus does a few things very well: he generates a lot of ground balls and limits hard contact. He has been hindered by poor control and a hittable sinker.

Recently, he has increased his cutter usage, which has been a very efficient pitch for him. A harder knuckle curve and a new splitter may be pluses to his arsenal. In 2024, de Geus has seen an increase of velo on all of his pitches, helping him have a bit more whiff. 

This pie graph shows the pitch usage for de Geus this season in AAA. In addition to his sinker and cutter, his knuckle curve also generates soft contact on the ground. I suspect we see de Geus have another increase in cutter usage, surpassing his sinker, which is something many teams have started to do over the past couple of years because the cutter offers the upside of being able to get players to swing and miss. 

de Geus is much more of an east-to-west pitcher than north-to-south. If he can locate his cutter in to lefties as he does and away from righties and vice versa with his sinker while mixing his offspeed pitches to keep batters off balance, he should be able to stop loud contact. Leaving the ball over the plate normally hurts anyone, but especially De Geus. The Marlins must find a way to get the 26-year-old to command the ball.

This heat map shows in 2024 where the damage against him has been. Balls in the middle of the plate or higher get hit hard.

The Marlins added a project who has had an uptick in velo, a new pitch, and the ability to limit hard contact and get balls on the ground with a funky release and barely one year of MLB service time under his belt. I believe there is an up arrow next to Brett de Geus.