※ 引述《spurs2120 (Fundamental)》之铭言： : 标题: Re: [心得] 为什麽Duncan的火锅比Howard来的有价值 : 时间: Thu Nov 24 23:30:38 2011 : : → bahamutuh:但把DH的火锅价值评分为最後一名 这计算一定有问题 11/24 22:33 : 推 bahamutuh:当一个结论出现很大争议时 那代表他的计算方式要改变 11/24 23:05 : → bahamutuh:DH的火锅价值评为最後一名 这应该没啥人会赞同 11/24 23:06 : 推 bahamutuh:DH的火锅价值只有总数？ 你只看这个吗 那我蛮失望的 11/24 23:10 : 推 bahamutuh:TD的防守能力是可以当一个球队的基石 11/24 23:16 : → bahamutuh:DH的补防范围和能力 却是TD比不上的 11/24 23:17 http://probasketballtalk.nbcsports.com/2010/11/04/dwight-howard-will-continue-blocking-shots-out-of-bounds-thank-you-very-much/ 我们看一下到底DH的分数为什麽会这麽低， 以及他自己是怎麽面对这个问题好了。这比鬼打墙来得有建设性一点。 Because of Howard’s tendency to swat shots out of bounds rather than tip them to his teammates and his high rate of goaltends, Huizinga found that Howard, on a block-by-block basis, had the least valuable blocks in the entire NBA. Howard’s goaltending was a much bigger issue than his tendency to swat shots out of bounds in the study, and I don’t think anyone would argue that goaltending is bad, including Howard. However,... “They told me to grab them, but sometimes blocking a shot and sending it out of bounds shows a team it’s not going to be easy to come in the paint,” Howard said. “Grabbing it, that’s like being a showoff or something like that, even though it is kind of cool.”So not only is Howard trying to block shots, he’s trying to make defenders shy away from him later in the game. He wants to send a message. “Every block,” he says. Howard might have a point, because Magic opponents have been absolutelyx terrified to take the ball to the rim this season. According to HoopData.com, the Magic only allow 15 shot attempts at the rim per game, which is the lowest mark in the NBA by a significant margin... 好了，在这一点上，DH有可能是对的。 但不让对手在内线得手跟团队打法有没有关系呢？显然不可能没有。 跟某人不断提及的补防范围，例如盖三分跳投有没有关系呢？答案显然是没有。 最後还是回到对对手的心理威胁，也就是霸气上。 到最後这篇新闻还是承认： It’s impossible to give intimidation an exact statistical value. 霸气是无法测量的，即使有时候我们找不到别的解释。 统计不是万能，但如果不能看到统计的优点而只能用一些似是而非的理由胡扯， 那真的没有什麽讨论的价值。 --

※ 发信站: 批踢踢实业坊(ptt.cc) ◆ From: 99.125.165.60 ※ 编辑: Alfred 来自: 99.125.165.60 (11/25 00:47) 在进一步谈DH跟goal-tending以前， 我们先搞清楚到底这个数据是怎麽去评断一个火锅的价值。 这里有个很简要清楚的summary： http://thinkbluecrew.blogspot.com/2010/08/anatomy-of-block-introduction-part-1.html A study by a professor at the University of Chicago Booth School of Business named John Huizinga (you may know him as Yao Ming's agent) shows that, no, not all blocks are equal. At this year's MIT Sloan Sports Analytics Conference, Huizinga presented a paper titled "The Value of a Blocked Shot in the NBA: From Dwight Howard to Tim Duncan." In it, Huizinga explains how he and Sportsmetricians Consulting's Sandy Weil developed a database called Chances, using data provided by STATS, LLC. to compile the context of each event for the past 7 years, events such as blocks. The idea for this database is simple: instead looking at box scores, look at play-by-play accounts of the game in order to ascertain individual offensive opportunities. As Sandy Weil explains at his website, the two believe that "chances" are a very useful unit of account for many types of analysis of basketball. It allows you to easily sort and filter the context of an event, for instance, what happened before a shot attempt or what happened after a steal. One of the key concepts that Huizinga presented about in order to understand the value of blocked shots was the preblock situation. This is basically what happened before the block occurred. As Sebastian Pruiti explains at NBA Playbook, this allows the analyst to differentiate between a block of a layup coming off a fast break opportunity vs. a block of a long off-balanced two-point jump shot, understanding that the former is more valuable than the latter. The idea that these two types of blocks are different comes from the fact that all shots taken have its own values, whether the shot was a slam dunk or a turnaround jumper. This leads us to expected point value, and since every block is attributed to a shot, the value of a block is naturally related to the expected point value of the shot attempt. Looking at Pruiti's recap of the presentation, Huizinga closed his thoughts by going over what he calls "block value." To quote Pruiti, "to determine block value, Huizinga used the formula Points Saved + Points Created where Points Saved equals the effect of a Block on Opponents Expected Points during this possession and Points Created equals the effect of a Block on Own Team’ s Expected Points during the next possession." This formula allowed Huizinga to determine overall block value, a better indicator of who was the best "shot blocker" in any given season. 上色部分已经很清楚的点出这个资料库的特色以及火锅价值的判断原则， 基本上判断的对象包含两阶段： 1.Points Saved = the effect of a Block on Opponents Expected Points during this possession 所谓火锅发生时的状况（preblock situation）必须纳入考量， 这是为了更精确的计算这个火锅到底阻止了什麽， 很明显，这并不只是单纯用跳投与非跳投来计算，而有更细部的公式， 跳投与非跳投的期望值只不过是个出发点。 为什麽要用期望值而不直接用两分或三分出手来算， （所以什麽+2 -2甚至-4之类的都显然是在胡扯。） 稍微有点统计常识的人都知道应该不需要另加解释。 2.Points Created = the effect of a Block on Own Team’s Expected Points during the next possession 火锅发生後的状况，也就是火锅的结果在下一个possession造成的效应。 在此最关键的因素就是球权究竟谁属， 事实上若参考Sandy Weil在他的blog的文章， 他甚至还会去区分球权是在alive的状态直接转换於守方或回到原攻击方手上， 还是因为出界、goal-tending或其他因素而转换或回到原攻击方手上， 为什麽要去看球权的转换，仍究是为了判断在这个possession攻方得分的期望值。 换言之，火锅的价值就在於这个动作对双方得失分的期望值的影响上， 以篮球这项运动来说，这是相当合理的出发点， 即便这个模型不能解释球场上所有的事情，也是相当值得参考的一个发展。 那为什麽几乎所有人都一致同意goal-tending是个bad outcome？ 因为当goal-tending发生的时候，shot attempt的命中率已经完全不重要， 由於防守方失败的介入，其Point Saved以100%的机率让对方得分， 根据这个网站的引述： http://probasketballtalk.nbcsports.com/2010/03/09/dwight-howards-defense-is-overrated-except-for-when-it-isnt/ “If your block produces an offensive rebound — often the result of smashing the ball out of bounds — that’s neither the best nor worst result. The other team keeps the ball, with an expected value of about 1 for its possession. If you goal-tend on a block, that’s the worst; your opponent scores automatically, and occasional fouls push the expected value of the possession up to about 2.07. Over the entire stretch of data that Huizinga and Weil examined, Tim Duncan didn’t goal-tend once, while 24 percent of Dwight Howard’s blocks resulted in free points for the other team.” 换言之，不但没有save到任何分数，对方得分的期望值因为犯规的可能性甚至高达2.07。 而DH的火锅里有24%都是这个下场，分数低落是当然的结果。 去争论goal-tending的好坏是没有意义的，因为goal-tending是个结果， 从定义上它就是直接造成球队的损失， 而且没有增加球队在下个possession得分的期望值。 这跟抄截与失误的关系很像，积极的盖锅行为本来就带有风险， 而眼睛不能只看到积极进取的所谓吓阻力，而没有看到风险实现时对球队的损害。 在这里AI又是个好例子， 因为AI的防守评价与那些抄截王与接近抄截王的数据间的关系已经有很多讨论， 相信很容易就能找到，在此不多说。 因此，积极的盖锅行为当它成为火锅的时候，依照前面的原则自然会有其相应的评价， 而当他成为goal-tending的时候，自然也就应该依照同样的原则进行评价。 至於说是积极也好，说是冒险也好， 盖锅的出手判断本身并没有直接对这个公式有所影响的理由。 当然，这个数据出来之後针对DH有不少讨论， 前面引的这个网站 http://probasketballtalk.nbcsports.com/2010/03/09/dwight-howards-defense-is-overrated-except-for-when-it-isnt/ 就有不错的讨论， 另外 http://insider.espn.go.com/insider/blog?name=keating_peter&id=4978827 这篇文章也是经常被引用，但是需要帐号才能看。 给有兴趣的人参考。 ※ 编辑: Alfred 来自: 99.125.165.60 (11/25 15:42) 最後补充总板animos大写信给Sandy Weil所得回覆作结： #1EqZ9QUs (NBA) " The 2.07 you reference is what we estimated as the points given up by goaltending a non-jumper. (The value for a 2-pt jumper is actually 2.08, and your 60-ft jumper case would be 3.00 points.) But then we subtract from that a points saved value: the expected value for the shot that was blocked. We refer to it as the expected value of the counter-factual--what did not happen. We provide those expected values one slide earlier in our presentation. See table below. Basically, the cost of goaltending a non-jumper that occurs in a chance that began with a live-ball turnover is -2.07 (points you cost your team) minus 1.70 (the points you saved your team) equals - 0.37. That is the value of that particular goaltending--you cost your team about 0.37 points versus not challenging the shot / attempting to block it." 换言之，DH的分数是在已经采取对goal-tending价值认定较宽的算法下所得， 这份统计并非像某位仁兄所说的不足采信。 ※ 编辑: Alfred 来自: 99.125.165.60 (11/27 22:28)