Certain quantificational elements (“interveners”) have long been known to disrupt the interpretation of wh-in-situ (Hoji 1985 and many others), but the correct description of the set of interveners and the nature of intervention effects have been the subject of continued debate. We present a new generalization concerning the nature of intervener-hood in Japanese: A quantifier acts as an intervener if and only if it is scope-rigid. We follow the view that intervention effects reflect a particular LF configuration (Beck 2006 a.o.), but in contrast to previous approaches, we propose that any DP can lead to intervention if it is interpreted in a derived position above a wh-phrase at LF. Quantifiers which appear to be non-interveners are able to avoid this configuration. Intervention is limited to quantifiers interpreted in a derived position via movement, which supports the theory of intervention effects developed in Kotek 2017 as reflecting a logical incompatibility between the Predicate Abstraction rule and the computation of Rooth-Hamblin alternatives.