Every fantasy baseball owner is typically caught in a dilemma after the season’s first month. He has to judge whether a surprising player’s hot start is valid or deceptive and then shift his roster accordingly.

Here are examples — at three different positions — of players heading in opposite directions:

Starting pitchers

Valid: Jaime Garcia, St. Louis
Learn to love ground-ball pitchers such as Garcia. He’s induced 10-plus grounders in four of his five starts, so his ability to keep the ball on the grass makes up his for mediocre 6.5 K/9 rate. He’s also a good bet to earn double-digit wins with support from the Cardinals’ solid defense and batting order.

Deceptive: Phil Hughes, Yankees
Hughes is a strikeout threat as evidenced by his 8.6 K/9 rate. But his 1.44 ERA and 0.88 WHIP could rise substantially based on three factors: opposing hitters’ poor luck, too many fly balls and a 4.3 BB/9 rate. He’s lucked out by serving up just one homer despite permitting 30 fly balls already, according to FanGraphs.com. That luck could turn along with batters hitting just .122 against him.

Third basemen

Valid: Alberto Callaspo, Kansas City
Callaspo is giving the Royals the type of batting production at the hot corner they were hoping to get from the demoted Alex Gordon. Callaspo hit .300 in a full-time role last year at second base and the same mark is within reason this year. Watch out for 40-plus doubles and double-digit triples and home runs now that he’s reached his baseball prime at age 27.

Deceptive: David Freese, St. Louis
Good as he is defensively, Freese can’t be expected to continue his offensive production, which includes a .358 average and 19 RBIs. His batting average on balls in play is .433 and he is hitting just .231 with a lowly .535 OPS on the road. The 27-year-old rookie is a late bloomer in the big leagues; his inexperience might lead to extended hitting slumps.

Outfielders

Valid: Marlon Byrd, Chicago Cubs
The Cubs finally scored on a free-agent signing. Byrd, previously with Texas, has hit at least .283 in the four previous seasons he’s had at least 400 at-bats, so his .354 batting average shouldn’t decline by much. Batting at cleanup and in the fifth spot should ensure he accumulates 80-plus RBIs for the second straight campaign.

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Deceptive: Austin Jackson, Detroit
Before you salivate too much over his .377 batting average, note that Jackson has a completely unsustainable .532 average when he puts the ball in play. Given that the former Yankees prospect strikes out on almost 30 percent of his at-bats and takes a walk in only 8 percent of his plate appearances, Jackson is ripe for a major rookie slump sooner rather than later.