SCOTTSDALE — During spring training, especially the first couple of weeks, it can be difficult at times to tell if a player is preparing for Opening Day or just trying to pass the time on a hot day in the desert. It’s common to see infielders and catchers shag fly balls and outfielders try to scoop a few grounders at short. For years, former Giants shortstop Brandon Crawford would celebrate the start of camp by hopping on the mound at Scottsdale Stadium and throwing a few pitches. When Bryce Eldridge planted himself in left field during batting practice on Wednesday, it at first looked like he was joining others in simply watching his teammates hit. But soon Eldridge started working on his pre-pitch routine and jumps and getting tips from Drew Gilbert. If Eldridge makes the Opening Day roster, he’ll play first base and DH for the Giants. But they also know they might have a pretty inflexible roster with two first base/DH types, along with Luis Arraez, who mostly played those spots last year. It makes sense for the 21-year-old Eldridge to gain some versatility, and manager Tony Vitello told him recently that he should do some work in left...