A Study to Evaluate the Efficacy, Safety, and Pharmacokinetics of Prophylactic Emicizumab Versus no Prophylaxis in Hemophilia A Participants With Inhibitors

Inclusion Criteria:

* Body weight \>/= 40 kilograms (kg) at the time of screening
* Diagnosis of congenital hemophilia A of any severity and documented history of high-titer inhibitor ( that is \[i.e.\], \>/= 5 Bethesda Units \[BU\])
* Documentation of treatment with episodic or prophylactic bypassing agents for at least the last 24 weeks
* \>/= 6 bleeds in the last 24 weeks prior to screening (if on an episodic bypassing agent regimen) or \>/=2 bleeds in the last 24 weeks prior to screening (if on a prophylactic bypassing agent regimen)
* Adequate hematologic, hepatic and renal function
* For women who are not postmenopausal or surgically sterile: agreement to remain abstinent or use single or combined highly effective contraceptive methods

Exclusion Criteria:

* Participants with inherited or acquired bleeding disorder other than hemophilia A
* Participants with ongoing (or plan to receive during the study) immune tolerance induction therapy or prophylaxis with Factor VIII (FVIII), with the exception of participants who have received a treatment regimen of FVIII prophylaxis with concurrent bypassing agent prophylaxis
* Previous (in the past 12 months) or current treatment for thromboembolic disease (with the exception of previous catheter-associated thrombosis for which antithrombotic treatment is not currently ongoing) or current signs of thromboembolic disease
* Participants with other conditions (for example \[e.g.\], certain autoimmune diseases) that may increase the risk of bleeding or thrombosis
* History of clinically significant hypersensitivity associated with monoclonal antibody therapies or components of the emicizumab injection
* Known human immunodeficiency virus (HIV) infection with cluster of differentiation 4 (CD4) count \< 200 cells per microliter (cells/mcL) within 24 weeks prior to screening
* Use of systemic immunomodulators (e.g., interferon or rituximab) at enrolment or planned use during the study, with the exception of antiretroviral therapy
* Participants who are at high risk for thrombotic microangiopathy (TMA; e.g., have a previous medical or family history of TMA), in the investigator's judgment
* Concurrent disease, treatment, or abnormality in clinical laboratory tests that could interfere with the conduct of the study or that would, in the opinion of the investigator or Sponsor, preclude the participant's safe participation in and completion of the study or interpretation of the study results
* Planned surgery (excluding minor procedures such as tooth extraction or incision and drainage) during the study
* Receipt of emicizumab in a prior investigational study; An investigational drug to treat or reduce the risk of hemophilic bleeds within 5 half-lives of last drug administration; A non-hemophilia-related investigational drug within last 30 days or 5 half-lives, whichever is shorter; An investigational drug concurrently
* Unwillingness to use highly effective contraception methods for the specified duration in the protocol (females only, unless required otherwise by the local health authority)
* Clinically significant abnormality on screening evaluations or laboratory tests that, in the opinion of the investigator, may pose an additional risk in administering study drug to the participant
* Pregnancy or lactation, or intent to become pregnant during the study

For more information on this trial, visit clinicaltrials.gov.