Why does it seem so hard for a player to play well when traded from one league to the other?

Hitters have to face to pitchers that they have rarely seen, as opposed to when they were in their same division and played the sames divisonal teams 80 times a season they get use to the same pitchers.

Same thing for pitchers as well. Except some say it is easier to pitch in the NL with out the DH.

In an offensive standpoint you're seeing new pitchers, many of whom for the first time. You should understand that batters and their coaches create entire programs around specific pitchers and hitters. If you watch a game and see a coach with a thick binder, thats all it is; scouting reports. Film can only go so far, you know? In thirteen games Adrian Gonzalez is hitting .250 for the bosox. Expect that number to climb as he gets more adusted to sabbathia's slider and david price's fastball.

in a defensive pitching stand point, you would have to assume that it would be easier to switch from one league to another. Like in my previous argument, these batters are seeing you for the first time, and they dont know how much your curve ball actually curves. Look at Sabbathia, who thrived in cleveland, then milwakee, then in new york. Look at cliff lee, who pitched well in Cleveland, philadelphia, texas, and again in philadelphia. Of course, there are some exceptions; Javier Vazqeuz? Talk about a bust for last year's new york yankees. If you look at his stats, he pitched very well in montreal [expos, NL], sub par in his first year with the yankees, decent with the white sox, breakout year with atlanta, and shi* the bed with new york his second go around. He's currently with the marlins, and should probably be a national league pitcher.

In any case, I believe the national league pitching is better than the American league, but the American league hitting is better than the national league.

Yes, Roy Halladay has struggled making the transition to Philly.

Because he knows he took a pay cut and therefore, performs less. I know if I was getting 17 million a year then got traded and getting paid only 10 million a year, I have no incentive to perform better. (hehehe)

It takes time for players to adjust to an all new opposition