here's the rub（回答）

回答が遅くなってしまいました。今回のUG先生からの指名内容はThere's the rub.というHAMLETに由来する表現において，「こする」というrubが「障害，困難」という意味を持つようになった経緯についてです。
cf. http://d.hatena.ne.jp/A30/20141004/1412380741
手持ちの辞書では手に余ったので，ネットの力を借りると以下のような解説を見つけました。

By rub, Hamlet means a difficulty, obstacle or objection — in this case to his committing suicide.
The origin is the ancient game of bowls (which Americans may know as lawn bowling; nothing to do with tenpin bowling). A rub is some fault in the surface of the green that stops a bowl or diverts it from its intended direction. The term is recorded first a few years before Shakespeare’s time and is still in use. It appears, too, in golf, in the expression rub of the green, which refers to an accident that stops a ball in play — hitting an obstacle or a bystander perhaps — and for which no relief is allowed under the rules.
cf. http://www.worldwidewords.org/qa/qa-the3.htm

lawn bowlingは「芝生の上で木の球をジャック（jack）と呼ばれる的の白球にできるだけ近づけるゲーム」（『スーパー・アンカー英和辞典』第4版，学研教育出版）のことで，上記の説明からrubは芝生とボールとの「摩擦」を指し，これが抵抗となってボールの軌道を妨げることから「障害」という意味を持つようになったことがわかります。（Koyamamoto）

Ichiro eyes place to reach 3,000 hits
To be sure, Ichiro is durable and in tremendous shape. He still fluidly runs the bases stealing 15 of them this year and scoring 42 times. Defensively, he is graceful playing both corner outfield positions, and with a season-long elbow injury suffered by Carlos Beltran and Jacoby Ellsbury's hamstring strain at the end, played a lot more than anyone expected for the second year in a row.
But here's the rub: His hit totals and plate appearances have deteriorated over the course of the years and his 102 hits in 385 plate appearance this past season were both by far career lows. At his current pace, he'll need a least one more full season and part of another to reach 3,000 Major League hits.
So that begs the big question: Is there a team out there willing to give him a chance to do it?
http://m.yankees.mlb.com/news/article/97284472/ichiro-eyes-place-to-reach-3000-hits
http://d.hatena.ne.jp/A30/20120610/1339335980