It happens in sports every year: athletes produce a magical season, but then quickly fall back to earth despite heightened expectations. Predicting that regression is far from an exact science, but when it comes to fantasy - and more specifically, to fantasy hockey - the ability to peg a player who's set for a decline can be the difference between winning and losing.

With that in mind, here are four players to be wary of this fall:

William Karlsson, C/LW, Vegas Golden Knights

Let's not over complicate things here, Karlsson came out of nowhere to take the league by storm in 2017-18 with a ridiculous offensive campaign highlighted by a slightly shocking 43 goals and 35 assists for Vegas.

All props to Karlsson and the Knights for a sensational inaugural season on the strip, but the likelihood of the speedy Swede even cracking 30 goals next year is relatively low. Especially when you consider that his highest output previous to last season was a lowly nine with the Columbus Blue Jackets three years ago.

Don't forget, Vegas has already lost the scoring punch of veteran snipers James Neal and David Perron, so opposing teams will focus their attention on shutting down Karlsson and linemates Jonathan Marchessault and Reilly Smith.

The addition of Paul Stastny alleviates some of the offense lost with Perron and Neal, but the book is out on both the Knights and Karlsson, so the diminutive forward will be in tough to repeat last season's improbable offensive showing.

Dustin Brown, LW/RW, Los Angeles Kings

Speaking of guys who came out of nowhere last year, Brown had a resurgent 2017-18 that saw him surpass the 40-point mark for the first time in five seasons. While Brown's 28 goals and 33 assists were huge fantasy assets, his recent track record leaves some cause for concern.

It should also be noted Brown had the benefit of playing alongside a red-hot Anze Kopitar for a majority of last season, so his offensive numbers clearly benefited from the Hart Trophy-type campaign from his All-Star centerman.

Brown will likely have the same opportunity to play on Kopitar's wing next season, but expecting both players to repeat their production, especially Brown, is a risky bet. After all, the Kings are a team which perennially finishes in the bottom half of the league in team scoring.

Banking on a soon-to-be 34-year-old with rapidly diminishing foot speed to post back-to-back 40-plus point seasons for the first time in seven years would be a foolish move. Brown regresses next season, book it.

Josh Bailey, LW/RW, New York Islanders

Bailey's proven he can hang in the NHL over the last two seasons after posting 127 points over 158 games while holding down a spot on the Islanders' top line. However, that No. 1 line had been anchored by superstar pivot John Tavares over recent years, so Bailey's numbers are set for a significant decline with Johnny T now cemented in Toronto for the foreseeable future.

Tavares converted 29 of Bailey's 96 assists since the start of the 2016 campaign, meaning just over 30 percent of Bailey's apples came on JT's goals. Moreover, Tavares assisted on 14 of Bailey's 31 goals over the last two years, so, to expect Bailey to post another All-star-worthy season would be a bold prediction.

Now, Bailey will still have the benefit of playing with up-and-coming stars like 40-goal man Anders Lee and reigning Calder Trophy winner Mathew Barzal, so he still holds fantasy value, especially in deeper leagues. But without his talisman up the middle, Bailey will be hard-pressed to repeat last season's 71-point performance.

Phil Kessel, RW, Pittsburgh Penguins

No one likes to crush hot dogs and put up solid offensive seasons as much as Kessel does. But in all fairness to Phil, the impressive 92-point showing from last year won't be replicated in 2018-19.

Sure, he's coming off the most productive campaign of his 11-year career (34 goals and 58 assists), but Kessel will be turning 31 in October and it's not exactly like he's been the most committed player off the ice, either. Not to mention the rumored rift between Kessel and team management, which led to reports indicating Kessel was so unhappy with the Penguins that he would accept a trade out of Pittsburgh.

Related: - Report: Kessel not opposed to trade, would play for Tocchet's Coyotes

There is no denying the stellar season Kessel had in 2017-18, a career year is a career year no matter how you slice it. But Phil managed only one goal in 12 playoff games, and was clearly uncomfortable with how head coach Mike Sullivan was utilizing him in the postseason.

Kessel can still bring it, but given the potentially sticky off-ice situation and the growing notion that the veteran is getting tired of the day-to-day grind that comes with being an everyday NHLer, and it becomes quite evident that Kessel won't be posting another 90-point season.

(Photos courtesy: Getty Images)

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