Best shape of his life
Everyone wants to believe that when player X says that he tweaked his offseason workout routine, it's a sign of better things to come. He gained 20 pounds of muscle? He's primed to hit 30 home runs! He lost 15 pounds? He'll steal 50 bags! He took up an advanced stretching regimen? He'll play in 160 games! It's hard to resist the allure of believing claims that over the idle months the players have become better, faster, stronger. We've already had a Rockie bring up this particular canard, as Rex Brothers has reportedly showed up to camp 10-12 pounds lighter.
Of course, while physical fitness is important, these "best shape ever" claims usually aren't a surefire indicator of greatness to come. Lest we forget, these guys were already pretty good athletes the year before. And having a little bit more pectoral mass won't help you see an 88 mph slider any clearer (except for the subsidiary cliche: I got Lasik!). BSoHL is superior to "showed up to camp 50 pounds overweight," but don't let it alter your expectations too much.
Learned a cutter
Pitcher X got rocked last year. Never fear, though, he tinkered with a new grip in the offseason and now he has this killer cutter that will turn it all around. Somehow the cutter became the magic pitch of recent years; half fastball, half slider, all sexy. Pitcher X swears it will keep hitters off balance and induce ground outs galore. Might as well hand him the Cy Young award now.
One can't help but wonder: if the cutter were so dominating, why aren't all pitchers using it? Why aren't we in a league full of Mariano Riveras, with each game ending 1-0? Learning a new pitch might be useful, but there are only so many ways a person can spin a baseball. Major League hitters have seen it all before, so at the end of the day the formula for success remains the same: velocity, location, movement, and unpredictability.
More settled personal life
Player X was dealing with a difficult divorce last year. Player Y's father was in the hospital. Player Z was involved in contentious litigation. They simply couldn't concentrate while on the field. But all of that is behind them now, and they're ready to focus on their games 100%. They have rededicated their focus to their games, and big years are surely ahead.
Acquired magical amulet
We've all heard it before; player X found the rune of Xanthar in a cave in Indonesia. It bestows an aura of power and focus upon all who wear it, provided they prove their mettle in the field of battle. With Xantharian power at his back, player X is bound to receive MVP votes.
It may be tempting to believe, but it's wise to remain skeptical. Most amulets and talismans are cheap forgeries, created by local merchants to con unwitting tourists. Even the genuine articles are more likely to curse the player than provide him with occult strength; players end up reporting to camp with stunted flipper-arms instead of added muscle mass, which ends up taking weeks of therapy to fix, and requires lengthy DL stints. And the risk of waking undead zombie hordes is simply too high to make amulet theft a viable offseason strategy.
They're still more useful than Phiten necklaces though.
Has been replaced by robot
Player X has been in decline the last few years, as that old nemesis, aging, takes its toll. A former star, he's now a role player at best (but still being paid like an All-Star). Not to worry: an insane scientist has used his DNA and biometric robotics to make an exact robot replica, free from the limitations of our puny, unevolved flesh. With the singular focus of an unthinking, unfeeling machine, player X's robot proxy will return to his glory years and propel his team to a playoff spot.
We would all love for our players to be replaced with robots. Players that are always out there. That cannot be bargained with. That can't be reasoned with. That don't feel pity, or remorse, or fear. That will absolutely not stop, ever, until they reach the playoffs.
The reality, naturally, isn't so rosy. Cybernetic organisms have an unfortunate tendency to start killing everything in sight. Additionally, they're terrible at interviews. It's likely that Major League Baseball is already working on a testing program to determine which which players are actually people and which are robots. And while the "human element" of baseball is largely an antiquated notion, if too many players start becoming robots the game might lose some of its charm and unpredictability.
Is in league with Satan
While Christianity might be the more popular religion amongst Major League Baseball players, it's always exciting to hear that a player has pledged his soul to Satan. Christianity is largely interested in rewards for the afterlife, and the Christian God is less likely to affect the outcome of such menial concerns as a baseball game. Satan though: he's a reason to get pumped.
For the mere cost of a soul, a player can receive all the material benefits his heart desires, including a renaissance on the baseball field. Who wouldn't trade their integrity and chance at immortal life for the opportunity to blast 35 dingers and make it onto SportsCenter on a nightly basis?
A word of caution about willingly damned baseball players though: there can be unintended consequences. The devil drives a hard bargain. It's possible that the player does indeed have a career year, while every other player on the team has an inexplicable bad year, leading to a last place finish (see A-Rod, Texas Rangers years). Additionally, there's a real possibility that a screaming Al Pacino follows the team everywhere, making it difficult to watch the game without muting it.
Forewarned is forearmed; enjoy the reports out of Arizona this spring without falling for the cliches!