The Detroit Lions should have a pretty good defense this year.

That’s a suggestion a lot of people have made this offseason in explaining why a team that won just six games last year could surprise in Matt Patricia’s second season as head coach, and one I’ve offered up myself as a reason to be optimistic for 2019.

But now that the offseason workout program is done – the Lions hold their final organized team activity of the spring on Thursday – it’s time to dive deeper into that claim and see if the biggest reason for hope does in fact match up with reality.

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The Lions were a decidedly middle-of-the-pack defense last year under Patricia, though they made indisputable strides as the season wore on. They finished the year 10th in total defense at 335 yards per game and eighth in pass defense (224.9 ypg), but didn’t fare quite as well in more meaningful statistics.

Patricia has long said that total defense is a poor measure of a team’s defensive worth and that the stat that matters most is points allowed. Well, the Lions ranked 16th in the NFL in scoring defense at 22.5 ppg and allowed 30 or more points on four different occasions.

In Football Outsiders’ weighted Defensive-adjusted Value Over Average ranking, a statistical measure of how a team’s defense compares to its peers, the Lions checked in at No. 22 in the NFL.

The Lions seemed to turn a corner defensively last season in late October, after they acquired Damon Harrison in a trade from the New York Giants. Harrison is one of the top run defenders in the NFL, and he gave the team something it desperately needed after Sylvester Williams flamed out in free agency.

Harrison had 50 tackles and 3.5 sacks in 10 games with the Lions, and the defense fared significantly better with him on the field. In 10 games after trading for Harrison, the Lions allowed just 20.2 points per game, a full touchdown less (26.3 ppg) then they allowed before his arrival.

Harrison’s presence wasn’t the only factor in the Lions’ defensive turnaround. Patricia runs a fairly complex system and in his first year as a head coach, it took players time to adjust to what they were being asked to do. Other key contributors like Romeo Okwara, Da’Shawn Hand and Tracy Walker also were either not with the Lions at the start of the year or rookies who saw their roles expand as the year went on.

But while we tend to focus on all the positives that led to the Lions’ improved play on defense, there were other factors that skewed the numbers favorably the Lions’ way.

The Lions tried hard to shorten games as the season wore on because they were so depleted offensively. With no Marvin Jones, no Kerryon Johnson, a banged-up Matthew Stafford and, for the last week of the season, no Kenny Golladay, the Lions didn’t stand a chance of winning many shootouts and thus played extreme ball-control football to try and keep their opponents off the field.

Patricia tends to favor that style anyway, but even the worst offenses in the NFL average 0.25 points per play, so by eliminating a drive per game with their offensive approach, it stands to reason the Lions bolstered their common defensive statistical rankings as well.

Statistically, perhaps the biggest reason to believe the Lions’ defensive improvements from 2018 are sustainable this fall is the extreme success they had against the run after Harrison’s arrival.

The Lions finished 10th in the NFL against the run despite being atrocious in that aspect of the game early in the season (they allowed 139.3 ypg rushing without Harrison, 92.5 ypg rushing with him). The top five and eight of the NFL’s top nine run-stopping teams last year all made the playoffs, and from a personnel standpoint, the Lions have the horses to shut down opposing running games again.

Harrison played at a Pro Bowl level last season, though he didn’t so much as garner alternate status for the game. Hand and A’Shawn Robinson showed plenty of promise in their first and third years, respectively, and the latter is in a contract year now. The Lions added one of the best run-defending right ends in football this offseason in Trey Flowers. And middle linebacker Jarrad Davis is coming off his first career 100-tackle season.

That group, though, as good as it is, highlights several of the biggest concerns with the Lions defense this fall.

First, Harrison and top cornerback Darius Slay stayed away from the team all offseason in hopes of landing new contracts. Nothing is imminent with either player, and there’s no knowing how they’ll react if they don’t get new deals – or what sort of shape they’ll be in for training camp. If either player sees his production fall off, it could spell trouble for the Lions.

Second, Flowers has not practiced with the team all spring as he rehabs from end-of-season shoulder surgery. There’s no reason to rush him onto the field in June, of course, but we are talking about a defensive lineman with a shoulder injury, and one who’ll need to get used to the new faces he’s lining up next to at some point.

Finally, none of the aforementioned players has ever been a big sack producer – Flowers, though he was the top defensive end available in free agency, has never reached double-digit sacks in college or the pros – and the Lions’ Achilles heel defensively still appears to be a lack of big-time playmakers.

The Lions did not have a player with more than 7.5 sacks last season, and their 14 total takeaways was second fewest in the NFL. Yes, they’ve stressed the need to create more turnovers this fall, but any farmer will tell you a horse is a horse and you can only milk a cow.

The Lions, to keep the farm metaphor going, have some pretty rich soil on the defensive side of the ball, ground that looks real good here in the NFL’s planting season.

There’s legitimate reason to believe the unit will build off the success it had in the second half of last year, and thus reason to be optimistic about the season ahead.

But know that the roots are still delicate, and there’s a chance they don’t take hold, which means the Lions could be in for another long winter.

Contact Dave Birkett at dbirkett@freepress.com. Follow him on Twitter @davebirkett. Read more on the Detroit Lions and sign up for our Lions newsletter.