English sentential subject extraposition is a marked feature, but it is quite a systematic structure. This study aims to provide an extraposition occurrence environment and a plausible trigger for the extraposition of a sentential subject. To this end, we first identify a total of 414 examples of COCA corpus, and then discuss their predicates as well as sentential types. An adjectival predicate (52.2%) is frequently employed without a strict semantic restriction, whereas that-clause (55.8%) and to-infinitival clause (35.5%) are mostly extraposed at the sentence-final position. From this corpus data, we suggest that the extraposition occurs across no more than the first complement of a head verb if and only if the complement is not a clause. In addition, the extraposition is assumed to be triggered in order to maximize focus effect (i.e., degree of pitch increase) rather than its grammatical weight, information structure, or BNFC constraint. The essence of the extraposition can be interpreted without solely grounds of the complex syntactic constituents or the discourse-new/old structures. In other words, in order to achieve a speaker's desired result to put an emphasis on a main predicate, he or she employs the rise of pitch on the main predicate, thereby extraposing a sentential subject.