A Study Evaluating the Efficacy and Safety of Pirtobrutinib in Participants With Relapsed or Refractory Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma

Inclusion Criteria:

* Have confirmed diagnosis of CLL/SLL as defined by iwCLL 2018 criteria.
* Part 1: Have received prior CLL/SLL treatment
* Have received at least 1, but not more than 3 lines of prior treatment for CLL/SLL
* Have received a covalent BTK inhibitor
* Part 2: Have received no prior treatment for CLL/SLL

  * Part 1 - Known 17p deletion status (positive or negative)
  * Part 2 - Must have 17p deletion (positive)
* Have a requirement for therapy consistent with iwCLL 2018 criteria for initiation of therapy
* Capable of swallowing oral study medication.
* Have an Eastern Cooperative Oncology Group Performance Status (ECOG) score of 0 to 2.

Exclusion Criteria:

* Have received prior treatment with a BTK degrader or a noncovalent BTK inhibitor
* Have a history of greater than or equal to (\>=) Grade 3 bleeding due to treatment with a BTK inhibitor
* Have known or suspected Richter's transformation
* Have known or suspected history of central nervous system involvement by CLL/SLL
* Previous or concurrent cancer distinct from CLL/SLL within 3 years before randomization. Exceptions may occur with documented sponsor approval. Examples include:

  * nonmelanoma skin cancer or lentigo malignant melanoma
  * cervical carcinoma in situ
  * localized prostate cancer undergoing active surveillance, and
  * localized (for example, lymph node negative) breast cancer with no evidence of active disease present for more than 3 years. Individual may be receiving adjuvant hormonal therapy