Against the Spread Trends & Analysis: The Impact of Injuries

- Matt Cox

The late, great Andy Williams is on record declaring the holiday season as the most wonderful time of the year - that take may ring true for the vast majority of us, but for the laundry list of college basketball players currently ailing with injuries, the spirit and joy of the holiday break is often tainted by dreaded rehab sessions and endless hours spent horizontal on the training table.

So at the risk of being an insensitive scrooge with no regard for the health of young athletes, let's get down to what us degenerates really care about - what this means from a gambling perspective.

Keeping track of who's in and who's out on a night-to-night basis can be maddening for college hoop bettors. Add in the wrinkle of the eligibility factor - specifically, players now becoming eligible for the 2nd semester - much like Santa and the elves prepping for Christmas Eve, you better check twice on who will be M.I.A. each night before putting that hard earned money at risk.

Fueled by my own frustration of keeping tabs with nightly lineup changes - along with a deep yearning to put some newly acquired historical ATS data to good use - I sought out to assess how well the bookmakers in Vegas account for the perpetually changing variable of game-to-game rosters. While a truly robust research study would look back multiple years to gain a more desirable sample size, my 'quick and dirty' analysis focused on last year only with the intention of identifying impact players who missed 5 or more consecutive games during any stretch of the season. I further narrowed my focus to the top-10 conferences according to (Power 6, AAC, A-10, MVC & MWC) for the final pool of impact players to pluck from.

Defining "impact player" is a slippery slope, but I tried to be somewhat systematic by targeting guys who played at least 30 minutes a game when fully healthy and/or eligible AND were relatively high usage contributors when on the floor. I think most reasonable college basketball fans would qualify all of the players shown in the charts below as "impact players".  Here are the two relevant test groups that were examined:

1) Players who missed time and then returned to action because they either became healthy or became eligible (went from not playing to playing)
2) Players who were in the lineup and then went down with injury (went from playing to not playing)

The players highlighted in light brown fall into both categories - in other words, they played both before and after missing a significant chunk of the year (at least 5 games) and thus we can use their cases in both test sets.

We'll start first with looking at how teams performed against the spread when a key cog was inserted back into the rotation after missing time due to injury or eligibility...

While there appears to be a teensy bit of value for betting on teams immediately after a critical piece returns to the lineup (refer to first 3 games record), this sample from the 2016-17 campaign indicates Vegas is pretty damn good at what they do (shocking!).

If you isolate each example on a case-by-case basis, you can rationalize the results with some reasonable intuition. For example, it's no secret how vital Sindarius Thornwell was to the Gamecocks' magical Final 4 run, given he led his team in points, assists, rebounds AND steals last year (South Carolina went 3-0 and 4-1 against the number after his return in his first 3 and 5 games back, respectively). But not all impact players are created equal and many failed to move the needle as much as Thornwell did - see Michigan State going 2-3 after Miles Bridges returned to the lineup or Illinois State losing their first 3 ATS after Mikyle McIntosh rejoined the team late in the season.

The takeaway - which is further validated in the 2nd test group below - is that blindly wagering on any and all teams with a major piece back in the puzzle is just not a profitable betting strategy (albeit, I'd feel more confident in this assertion with a larger sample size)...

BUT, as I alluded to above, on a case-by-case basis, there are certainly instances where the presence of a do-everything guy like Thornwell lifts a team's recent performance above Vegas' expectations, just as there are counter examples of players whose presence may be overvalued - refer to Arizona's lackluster ATS record after Allonzo Trier came back and then ask diehard Arizona fans and NBA scouts about Trier's defensive shortcomings, which is backed up by the advanced on/off data provided by (see below):

While we called out some intriguing examples in the first test group above, there were even more head scratching results produced by the second test group (see below) - to reiterate, these are the against the spread records for each team after a key player went down with an injury and missed 5 or more consecutive games immediately following that injury:

Womp womp - it sure is frustrating when the data fails to tell us anything groundbreaking, but these findings should prevent us from making any knee jerk, "auto-fade" betting decisions against teams that lose a critical contributor to an untimely injury. Hell, in many cases, 'the Ewing Theory' was applicable as teams actually benefited from the 'addition-by-subtraction' phenomenon - again, relative to Vegas' standards...

Virginia Tech went on a 5-game tear for their betting backers after one of my favorite players in the ACC, Chris Clarke, went down for the season. And just like so many Tom Izzo coached teams, Michigan State started to hit their stride down the stretch, which coincided with the loss of Eron Harris for the rest of the year. An especially bizzare result was how East Carolina started to right the ship after the loss of talented veteran wing BJ Tyson in the 18th game of the regular season (4-1 ATS in the first 5 games after he went out), but then were equally as profitable right after Tyson returned 7 games later (see 1st chart above). Turns out ECU was an against the spread darling all season long, regardless of whether or not their best player (debatably) was in the lineup.

One of the better resources we've found to track injuries across the entire college basketball landscape  is We highly recommend bookmarking this site and doing a quick cross check of local reports to ensure you know exactly who is and isn't playing throughout conference play.