Fantasy baseball addicts are the ambulance chasers of the sports world. Spy a significant injury, and off they scurry, nary a tear shed, to be the first to sign his replacement.

The Wilson Betemit sweepstakes began at exactly 6:14 p.m. last Sunday, when news of Chipper Jones’ injury hit the wires. But how do you know when the ambulance chasing is warranted, and when it’s in vain?

It’s all about opportunity and upside.

Will the injury keep a starter out for a significant amount of time, and can the replacement do anything with the playing time?

This week, the bloodthirsty fantasy mavens quickly found the Braves’ Betemit and, when Coco Crisp went down due to a finger fracture in Boston, Wily Mo Pena. Either may be a good stopgap, but I believe only one of them (hint: not the one who tips home run balls into the Fenway stands with his glove) is worthy of serious consideration.

Regardless, the biggest issue is to exercise judgment about who will be dropped in order to get those replacement at-bats. It’s been said that a fantasy owner can’t win a league in the first month, but easily can lose one. Among the players I’ve seen dropped by overzealous fantasy owners in the first two weeks this season: Brian Giles, Javy Lopez, and Bartolo Colon.

If you learn nothing else from this column (this is quite possible), remember this: Friends don’t let friends drop Bartolo Colon, no matter who the replacement player is.

Rising stars

Wilson Betemit, IF, Braves

As it turns out, Jones’ knee and ankle injuries don’t appear to be as serious as they originally had appeared. He could return as soon as he’s eligible to come off the disabled list, the last week of April.

That doesn’t matter. We’re enamored with Betemits’ potential. The 25-year-old infielder is a super sub, a guy who not only can play a bunch of different positions, but can hit enough to be a star in his own right. The 25-year-old infielder is still developing, but his .305 average last year in 246 at-bats was no fluke, and he has the power to dwarf the four home runs he hit.

Eligible at shortstop, Betemit is a good pickup for mixed AL/NL leagues. Stash him on your bench in case fragile Chipper goes down again.

Alexis Rios, OF, Blue Jays

This isn’t based on an injury, just a hot start that shows us how good this unheralded outfielder can be. While Eric Hinske will steal some of his at-bats, the Jays love Rios and will be only too happy to pencil him in every day if he keeps hitting like this. He’s off to a great start, hitting three home runs in his first 22 at-bats with an average over .400. He has speed (14 SB last year), and now that he’s batting second and not eighth, he’s in a good spot to showcase it. Rios is a burgeoning 20-20 performer. Grab him while you can.

Falling fortunes

Red Sox outfielders

Tread very carefully here. Crisp and Trot Nixon are out for a short time, and in their place are two all-or-nothing guys, the type who tend to excite fantasy owners.

Pena and Dustan Mohr are nearly the same player. Both can hit the ball a mile, and both did in their first starts of the year.

Unfortunately, both have struggled with breaking pitches and are wildly prone to striking out. Pena has whiffed nearly 300 times in fewer than 900 career at-bats; Mohr strikes out once every 31â2 at-bats.

So Pena may have as much power as any player in the game, but until he can hit a major-league curveball, he’s not a terrific fantasy option. No opportunity will change that. Mohr is unlikely to last with the team beyond a week or two.

Daniel Cabrera, SP, Orioles

The Orioles prospect/project nearly achieved an exceedingly rare baseball double-double in his second start, against Tampa Bay: 10 walks, 10 strikeouts. He fell one walk shy in five innings. He has wicked stuff, but even Leo Mazzone can’t seem to help him find a consistent release point. Its possible he’ll harness his considerable ability at some point and dominate, but Cabrera is a WHIP disaster. Let someone else ride this roller coaster.

Quick hits

Want a good two-start pickup for the week? Try Cleveland’s Paul Byrd, who will pitch at Detroit and at Baltimore. In his career, he has a sub-3.00 earned-run average combined at Camden Yards and Comerica Park. A guy like the Brewers’ Geoff Jenkins, who has no RBIs through his first 31 at-bats, could be available by trade. See if you can get a worried owner to bite on a 2-for-1 offer. Offer a Chris Shelton-type for Jenkins and a lesser 1B (Lyle Overbay?), and if they go for it, you’ll be smiling come July. Diamondbacks rookie 1B Conor Jackson is 4-10 with three homers in his career against the Rockies Jeff Francis. Against other pitchers, he’s 19-95 (.200) with no home runs. He may have a huge future, but for now, I’d say he’s an excellent play when he’s facing Francis. Otherwise, not so much.