We now move into a time frame in which a sizable number of fans will have tangible memories of actually seeing the players who appear in our first-half Top 300 list. (As always, remember that the list order here is determined by OPS+ rather than raw OPS, because the former takes into account league run scoring and ballpark effects...
We probably don't remember the really hot start that Harmon Killebrew had in '61--and we almost certainly don't recall that Jim Gentile was on fire in the early going of the 1960 season, a fact obscured by his more robust HR totals the following year. Finally, there's the apotheosis of George Altman, who had a couple of impressive seasons for the Cubs in the early 60s before doing a not-so-slow fade.
This table covers 1962-65, and note that no one cracks the Top 300 in '63, the year the strike zone changed. 1964 seems to be the year where a number of folks charged out of the gate with high-flying performances: both Willie Mays and Billy Williams were hitting over .400 in early June that year before drifting sharply downward in the intervening weeks before the All-Star break. We also see a half-year peak for the Twins' Bob Allison, whose career would soon be thwarted by injury. (Speaking of which, Mickey Mantle's highly ranked--#13--first half in '62 just barely exceeds our 200 PA cutoff. Despite this, it's a barnburner, with both a .500+ OBP and a .700+ SLG.)
Two terrific hitters--Dick Allen and Willie Stargell--make their first appearances on this list in '66, with Allen also popping up near the low end of the Top 300 the following year. Orlando Cepeda, who was somehow absent in his league-leading HR season (1961), makes a more 30s-style appearance on the list for his start in 1967, after his trade to the Cardinals. Carl Yastrzemski also had a great start for the Red Sox in '67 before his stalwart September that propelled Boston into the World Series for the first time in twenty-one year. That quiet superstar Al Kaline quietly cracks the Top 300 in both '66 and '67.
And whither Adolfo Phillips, a flash in the Cubs' pan? It would take nearly 40 years for the Cubs to get back to the World Series, and nearly 50 years for them to actually win it. Call it "the curse of the double leadoff/double cleanup man"...
As we get into the late 60s we see a trend for more games in April, which means that the number of games in the first half of the season often is in excess of 50%. That explains why we have two players--Reggie Jackson and Frank Howard--with 30+ HR first halves in 1969.
Howard, Willie McCovey and the ever-controversial Dick Allen are the hitters who show up in the Top 300 in both years. Some interesting new names make their only appearance on this list: Ken Harrelson, Rico Petrocelli, and Willie Horton (whose team, the Tigers, would win the World Series for the first time in twenty-three years).
Note also that all four of the players cracking the Top 300 in 1968 have BAs below .300.
Doing the usual category count to sum up the decade, we see no .400+ BAs on the list, and only 3 out of the 41 first-half performances in the Top 300 for 1960-69 cracking a .350 BA. There are six sub-.300 BAs, five of them in 1968-69. There's only one .500+ OBP (Mantle in '62), six .450+ OBPs, and 31 .400+ OBPs. You'll find only four .700+ SLGs, 14 .650+ SLGs, and 28 .600+ SLGs. (These will all be summarized into a table a bit later, just as we did previously for the second-half results.) We have four 30+ HR first halves (three of them occurring in 1969), nine 25+ HR first halves, and 25 with 20 or more HRs.