As you've probably heard, Brian Roberts hit eight home runs in April. That would be notable for any player, but of course it's most notable for Roberts because he hit only four home runs last season. I don't have any idea how many home runs Roberts will hit from May through September, but it's hard to think of another recent middle infielder who went from no power (as measured by home runs) to big power.
Perhaps I'm forgetting somebody, but the only name that comes to mind immediately is longtime A's shortstop Bert Campaneris. As my old boss Don Zminda once wrote, "Campaneris had tied a record when he hit his first major league pitch for a home run; he homered later in the same game to tie another rookie mark. But after that he became a singles hitter, totaling only 24 homers during his first six seasons, with a high of 6 in 1965. But then came 1970."
Indeed. In 1969, Campaneris hit two home runs in 135 games. This was the fewest home runs he'd ever hit in a season, but not so different from any of his other seasons that anybody noticed. And in 1970? Campaneris hit 22 home runs.
He hit five homers the next season, eight the season after that, and never again more than five in one season; in 1976, Campaneris hit one home run in 149 games.
I don't think Campaneris tells us much about Roberts. Both are obviously statistical outliers, and comparing one outlier with another isn't the quickest path to prognostical wisdom. When it comes to a player such as Roberts, I prefer to avoid predictions and instead sit back and enjoy the ride for as long as it lasts.