get/have somebody's number

ダルビッシュはイチロー率いるマリナーズが苦手なようです。
　　　　　　　　　　
Got your number: Mariners outfielder Ichiro Suzuki singles against Rangers pitcher Yu Darvish during the first inning on Saturday in Seattle. The Mariners won 7-0.
Hernandez, Mariners too much for Darvish
SEATTLE — Felix Hernandez dominated the Texas Rangers again.
Hernandez allowed three singles and struck out 12 in Seattle's 7-0 win Saturday.
"Those guys are dangerous," Hernandez said. "Just tried to throw on the corners."
Hernandez leads the majors in strikeouts with 140.
In two starts against the Rangers this season, he's allowed one run in 17 innings, struck out 19 and given up nine hits.
http://www.japantimes.co.jp/text/sb20120716a1.html

get/have somebody's numberは「正体を見抜く」という意味です（『オーレックス英和辞典』旺文社）。アメリカ英語の俗語で，基本的には性格や前歴，動機などについての真実を掴んだときに使われます（"to understand the way someone behaves"）。ここでは「手の内（投球の種類・クセ）は知れているぞ」という意味合いとなっています。（Sugiuchi）